The following are questions with answers taken from various Wikipedia articles. This is to highlight some relevant points on the subject—"The Origin And Formulation Of The Trinity Doctrine"—which people should understand before continuing the bible study. The answers are excerpt taken from the full articles written on the subject. You can readily study the full articles written on the subject by clicking on the source link after each answer. Note: The answers to the following religious questions are taken from various Wikipedia articles due to their neutral point of view principle.  http://en.wikipedia.org/wiki/Wikipedia:Neutral_point_of_view  However, it is still highly recommend that you search the internet for more information on the subject.

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2F.1   Who was credited with using the word "Trinity" , "person", and "substance" to explain that the Father, Son and Holy Spirit are "one in essence—not one in Person"?

From the Wikipedia article- Trinity, these are written:

Etymology
The English word Trinity is derived from Latin Trinitas, meaning "the number three, a triad".^[13] This abstract noun is formed from the adjective trinus (three each, threefold, triple),^[14] as the word unitas is the abstract noun formed from unus (one)

The corresponding word in Greek is Τριάς, meaning "a set of three" or "the number three".^[15]

Tertullian, a Latin theologian who wrote in the early third century, is credited with using the words "Trinity",^[19] "person" and "substance"^[20] to explain that the Father, Son and Holy Spirit are "one in essence—not one in Person".^[21]

About a century later, in 325, the First Council of Nicaea established the doctrine of the Trinity as orthodoxy and adopted the Nicene Creed, which described Christ as "God of God, Light of Light, very God of very God, begotten, not made, being of one substance (homoousios) with the Father".
Source: Wikipedia, Trinity, http://en.wikipedia.org/wiki/Trinity (as of Feb. 10, 2010, 06:01 GMT).

The origin of the word Trinity was Tertullian, a Latin theologian who wrote in the early third century, is credited with using the words "Trinity", "person" and "substance" to explain that the Father, Son and Holy Spirit are "one in essence—not one in Person".

2F.2   How did the doctrine of the Trinity came to be, if it is not explicitly stated and explained in detail in the Old and New Testament of the Holy Bible?

The following excerpts from Wikipedia articles are being presented to highlight some historical facts that are relevant to the origin and formulation of the doctrine of the Trinity:

From the Wikipedia article on the Arius, these are written:

The Arian controversy
Arius is notable primarily because of his role in the Arian controversy, a great fourth-century theological conflict that rocked the Christian world and led to the calling of the first ecumenical council of the Church. This controversy centered upon the nature of the Son of God, and his precise relationship to God the Father.

Beginnings
The historian Socrates of Constantinople reports that Arius ignited the controversy that bears his name when St. Alexander of Alexandria, who had succeeded Achillas as the Bishop of Alexandria, gave a sermon on the similarity of the Son to the Father. Arius interpreted Alexander's speech as being a revival of Sabellanism, condemned it, and then argued that "if the Father begat the Son, he that was begotten had a beginning of existence: and from this it is evident, that there was a time when the Son was not. It therefore necessarily follows, that he [the Son] had his substance from nothing. ^[7] This quote describes the essence of Arius' doctrine.

Although "Arianism" suggests that Arius was the originator of the teaching that bears his name, the debate over the Son’s precise relationship to the Father did  not begin with him. This subject had been discussed for decades before his advent; Arius merely intensified the controversy and carried it to a Church-wide audience, where other "Arians" such as Eusebius of Nicomedia and Eusebius of Caesarea would prove much more influential in the long run. In fact, some later "Arians" disavowed that moniker, claiming not to have been familiar with the man or his specific teachings.^[1] However, because the conflict between Arius and his opponents brought the issue to the theological forefront, the doctrine he proclaimed—though not originated by him—is generally labeled as "his".
Source: Wikipedia, Arius, http://en.wikipedia.org/wiki/Arius  (as of Feb. 12, 2010, 00:04 GMT).

From the Wikipedia article on the First Council of Nicaea, these are written:

The First Council of Nicaea was a council of Christian bishops convened in Nicaea in Bithynia (present-day İznik in Turkey) by the Roman Emperor Constantine I in A.D. 325. The Council was the first effort to attain consensus in the church through an assembly representing all of Christendom.^[2]

Its main accomplishments were settlement of the Christological issue of the relationship of Jesus to God the Father; the construction of the first part of the Nicene Creed; settling the calculation of the date of Easter; and promulgation of early canon law.^[3][4]

^{Source: Wikipedia, First Council of Nicaea, http://en.wikipedia.org/wiki/First_Council_of_Nicaea (as of Dec. 27, 2010, 19:23 GMT).}

From the Wikipedia article on the Trinity, these are written:

Origin of the formula

In 325, the Council of Nicaea adopted a term for the relationship between the Son and the Father that from then on was seen as the hallmark of orthodoxy; it declared that the Son is "of the same substance" (ὁμοούσιος) as the Father. This was further developed into the formula "three persons, one substance". The answer to the question "What is God?" indicates the one-ness of the divine nature, while the answer to the question "Who is God?" indicates the three-ness of "Father, Son and Holy Spirit".^[63]

The Confession of the Council of Nicaea said little about the Holy Spirit.^[62] The doctrine of the divinity and personality of the Holy Spirit was developed by Athanasius (c 293–373) in the last decades of his life.^[67] He both defended and refined the Nicene formula.^[62] By the end of the 4th century, under the leadership of Basil of Caesarea, Gregory of Nyssa, and Gregory of Nazianzus (the Cappadocian Fathers), the doctrine had reached substantially its current form.^[62]
Source: Wikipedia, Trinity, http://en.wikipedia.org/wiki/Trinity (as of Feb. 10, 2010, 06:01 GMT).

From the Wikipedia article on the Nicene Creed, these are written:

The original Nicene Creed was first adopted in 325 at the First Council of Nicaea. At that time, the text ended after the words "We believe in the Holy Spirit", after which an anathema was added.^[8]

It is traditionally believed that the Second Ecumenical Council held in Constantinople in 381 added the section that follows the words "We believe in the Holy Spirit" (without the words "and the Son" relative to the procession of the Spirit);^[9] hence the name "Niceno-Constantinopolitan Creed", referring to the Creed as modified in the First Council of Constantinople.

History
The Nicene Creed of 325 explicitly affirms the divinity of Jesus, applying to him the term "God". The 381 version speaks of the Holy Spirit as worshipped and glorified with the Father and the Son. The Athanasian Creed describes in much greater detail the relationship between Father, Son and Holy Spirit. The Apostles' Creed makes no explicit statements about the divinity of the Son and the Holy Spirit, but, in the view of many who use it, the doctrine is implicit in it.
Source: Wikipedia, Nicene Creed, http://en.wikipedia.org/wiki/Nicene_Creed  (as of Feb. 10, 2010, 05:04 GMT)

From the Wikipedia article on the First Council of Constantinople, these are written:

The First Council of Constantinople is recognized as the Second Ecumenical Council by the Assyrian Church of the East, the Oriental Orthodox, the Eastern Orthodox, the Roman Catholics, the Old Catholics, and a number of other Western Christian groups. This being the first Ecumenical Council held in Constantinople, it was called by Theodosius I in 381^[1][2] which confirmed the Nicene Creed and dealt with other matters such as Arian controversy. The council took place in the church of Hagia Irene from May to July 381.

Background
The Council of Nicaea did not end the Arian controversy which it had been called to clarify. By 327, Emperor Constantine I had begun to regret the decisions that had been made at the Nicene Council. He granted amnesty to the Arian leaders and exiled Athanasius because of Eusebius of Nicomedia.

Up until about 360, theological debates mainly dealt with the Divinity of Jesus, the 2nd person of the Trinity. However, because the Council of Nicaea had not clarified the divinity of the Holy Spirit, the 3rd person of the Trinity, it became a topic of debate. The Macedonians denied the divinity of the Holy Spirit. This was also known as Pneumatomachianism.

The proceedings
The council affirmed the original Nicene creed of faith as true and an accurate explanation of Scripture. This council also developed a statement of faith which included the language of Nicaea, but expanded the discussion on the Holy Spirit to combat the heresy of the Pneumatomachi. It is called the Nicene Creed of 381 and was a commentary on the original Nicene formula. It expanded the third article of the creed dealing with the Holy Spirit, as well as some other changes. About the Holy Spirit the article of faith said he is "the Lord, the Giver of Life, Who proceeds from the Father, With the Father and the Son he is worshipped and glorified". The statement of proceeding from the Father is seen as significant because it established that the Holy Spirit must be of the same being (ousia) as God the Father.

This Council's decision regarding the Holy Spirit also gave official endorsement to the concept of the Trinity. By the end of the 4th century, the Byzantine Emperor Theodosius "issued a decree that the doctrine of the Trinity was to be the official state religion and that all subjects shall adhere to it".
Source:  Wikipedia, First Council of Constantinople, http://en.wikipedia.org/wiki/First_Council_of_Constantinople (as of Feb. 10, 2010, 10:24 GMT).

THE ORIGIN AND FORMULATION OF THE TRINITY DOCTRINE
Based on the above references, we can make the following conclusions:

1. THE USE OF THE WORD "TRINITY" (Early Third Century):
   • The word "Trinity" was first used by Tertullian in the early third century, that is after 200 AD
   • John the Apostle died in about 100 AD, he was the last surviving of the Twelve Apostles, the only one to die a natural death and died around the age of 94.
     THUS, it took more than 100 years after the death of the last apostle when the word Trinity was first used.
     Please Note: 1st century is years 1 to 100, 2nd century is 101 to 200, 3rd century is 201 to 300 and 4th century is 301 to 400
2. THE GREAT CONTROVERSY (Early Fourth Century):
   • The Arian controversy came to exist after the death of the Apostles. In the early fourth century, a great theological conflict rock the Christian world. This controversy centered upon the nature of the Son of God, and his precise relationship to God the Father.
   • The debate over the Son’s precise relationship to the Father did  not begin with Arius. This subject had been discussed for decades before his advent; Arius merely intensified the controversy and carried it to a Church-wide audience.
     THUS, it is right to say that this great controversy came to existence after the death of the Apostles.
3. THE COUNCIL OF NICAEA IN 325 AD: 
   • The above Great Controversy led to the calling of the first ecumenical council of the Church in Nicaea in 325 AD. The First Council of Nicaea was a council of Christian bishops convened in Nicaea in Bithynia (present-day İznik in Turkey) by the Roman Emperor Constantine I in A.D. 325.
   • The First Council of Nicaea established the doctrine of the Trinity and adopted the Nicene Creed, which described Christ as "God of God, Light of Light, very God of very God, begotten, not made, being of one substance with the Father".
   • THE DIVINITY OF JESUS (325 AD):  For the time the Church through the Nicene Creed of 325 explicitly affirms the divinity of Jesus, applying to him the term "God". Thus, it was only in 325 AD that the Church declared the divinity of Jesus and call him God.
   • But, the Council of Nicaea said little about the Holy Spirit. The Council of Nicaea said nothing about the divinity of the Holy Spirit.
     Thus, by the year 325 AD the divinity of the Holy Spirit was not clear and not yet declared.
4. THE GREAT CONTROVERSY CONTINUES:
   • The Council of Nicaea did not end the Arian controversy which it had been called to clarify.
     • Up until about 360, theological debates mainly dealt with the Divinity of Jesus, the 2nd person of the Trinity.
     • Because the Council of Nicaea had not clarified the divinity of the Holy Spirit, the 3rd person of the Trinity, it also  became a topic of debate.
     •  The doctrine of the divinity and personality of the Holy Spirit was developed by Athanasius (c 293–373) in the last decades of his life.
5. FIRST COUNCIL OF CONSTANTINOPLE IN 381:
   • The Council of Constantinople in 381 was called to finally settle the great controversy regarding the divinity of Jesus, the 2nd person of the Trinity and divinity of the Holy Spirit, the 3rd person of the Trinity.
     • This council also developed a statement of faith which included the language of Nicaea, but expanded the discussion on the Holy Spirit.
     • It expanded the third article of the creed dealing with the Holy Spirit, as well as some other changes. About the Holy Spirit the article of faith said he is "the Lord, the Giver of Life, Who proceeds from the Father, With the Father and the Son he is worshipped and glorified".
   • THE DIVINITY OF THE HOLY SPIRIT (381 AD):
     • The statement of proceeding from the Father is seen as significant because it established that the Holy Spirit must be of the same being as God the Father.
       Thus it is clear that it took the Church 56 years after Jesus was declared God, that is in the year 381, that the Church Council also declared that the Holy Spirit is also God.
6. THE OFFICIAL ENDORSEMENT OF THE TRINITY DOCTRINE:
   • This Council's decision regarding the Holy Spirit also gave official endorsement to the concept of the Trinity. By the end of the 4th century, the Byzantine Emperor Theodosius "issued a decree that the doctrine of the Trinity was to be the official state religion and that all subjects shall adhere to it"

THUS, It took about 300 years (after the death of the last apostle) for the Roman Church to give official endorsement to the concept of the Trinity. When the Church through the Council of Constantinople in 381 AD gave its decision regarding the divinity of the Holy Spirit, it also gave official endorsement to the concept of the Trinity. Thus, by the end of the 4th century, the Emperor Theodosius "issued a decree that the doctrine of the Trinity was to be the official state religion of the Roman Empire and that all subjects shall adhere to it".

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