THE DEFINITION OF GOD'S UNITY:
"Unity" literally means "oneness." God is one Being, in contrast to many beings. There is one and only one God (monotheism) as opposed to many gods (polytheism).
There are three related words that should be distinguished:
(1) Unity-There are not two or more gods.
(2) Simplicity-There are not two or more parts in God.
HOWEVER:
(3) Triunity-There are three persons in the one God.
The Scriptures affirm God's absolute unity from the beginning to the very end. The oneness of the Godhead is one of the most fundamental teachings of Scripture. Topical evidences include the theological basis for God's unity and the historical basis for God's unity.
With that in mind, we progress into;
THE BIBLICAL BASIS FOR THE TRINITY:
The doctrine of the Trinity is based on two basic biblical teachings:
(1) There is one and only one God.
The biblical, theological, and historical evidence for God's absolute
oneness has been established in scripture and history. We shall now address the second biblical teaching...
(2) There are three distinct persons who are God: The Father, the Son, and the Holy Spirit.
Three Different Persons Are God: Father, Son, and Holy Spirit.
In addition to declaring God to be one in nature or essence, the scriptures affirm that there are three distinct persons who are God. All are called God, and all have the essential characteristics of a person. Personhood is traditionally understood as one who has intellect, feelings, and will.
All three of these characteristics are attributed to all three members of the Trinity in Scripture. Essentially, personhood refers to an "I," a "who," or a subject. Each "I" in the Trinity possesses (by virtue of its one common nature) the power to think, feel, and choose. Personhood itself is its I-ness or who-ness.
That Christ is God is affirmed in many passages and in many ways, both directly and indirectly. Yahweh is only used to refer to the one true God. No other person or thing was to be worshiped or served (Ex. 20:5), and His name and glory were not to be given to another.
Jesus prayed, "And now, Father, glorify me in your presence with the glory I had with you before the world began" (John 17:5)-this is an obvious claim for Christ's deity, for Jehovah of the Old Testament said, "My glory will I not give to another" (Isa. 42:8 NKJV). Jesus also declared, "I am the First and the Last" (Rev. l:l7)-precisely the words used by Jehovah in Isaiah 44:6. He said, "I am the good shepherd," (John 10:11), and the Old Testament said, "Jehovah is my shepherd" (Ps. 23:l ASV).
Further, Jesus claimed to be the judge of all men (John 5:27; Matt. 25:31), and Joel quotes Jehovah as saying, "There I will sit to judge all the nations on every side" (Joel 3:12). Likewise, Jesus spoke of Himself as the "bridegroom" (Matt. 25:lf.) while the Old Testament identifies Jehovah in this way (Isa. 62:5; Hosea 2:16). While the psalmist declares, "Jehovah is my light" (Ps. 27:l ASVJ) Jesus said, "I am the light of the world" (John 8:12).
Perhaps the strongest claim Jesus made to be Jehovah is in John 8:12 where He says, "Before Abraham was born, I am!" This statement claims not only existence before Abraham, but equality with the "I AM" of Exodus 3:14. The Jews around Jesus clearly understood His meaning and picked up stones to kill Him for blaspheming (cf. John 10:31-33). The same claim is also made in Mark 14:62 and John 18:5-6.
Jesus professed deity in other ways, one of which was by claiming for himself the perogatives of God such as forgiving sin (Mark 2:5). The scribes correctly responded with "Who can forgive but God alone?" afterwards. So to prove that His claim was not an empty boast, He healed the man, offering direct proof that what He had said about forgiving sins was true also. Jesus claimed, due only to God, the power to raise and judge the dead; boldly assumed for Himself powers that only God has; and claimed that he should be be honored as God.
Jesus Claimed to Be Messiah-God. The Old Testament teaches that the coming Messiah would be God Himself, so when Jesus claimed to be that Messiah, He was also claiming to be God. Jesus Claimed to Be God by Accepting Worship. The Old Testament forbids worshiping anyone other than God (Ex. 20:l-5; Deut. 5:6-9). The New Testament agrees, showing that men refused worship (Acts 14:13-15), as did angels (Rev. 22:8-9). But Jesus accepted worship on numerous occasions, revealing that He claimed to be God.
Jesus Claimed to Have Equal Authority With God. "All authority in heaven and on earth has been given to me. Therefore go and make disciples of all nations" (Matt. 28:18-19).
Jesus Claimed to Be God by Requesting Prayer in His Name. Jesus not only asked people to believe in Him and obey His commandments, but He also asked them to pray in His name: "And I will do whatever you ask in my name...You may ask me for anything in my name, and I will do it" (John 14:13-14).
Jesus Claimed to Be God by His Use of Parables. Jesus' Disciples Acknowledged His Claim to Be God. Etc... etc... etc...
All members of the Trinity are equal in essence, but they do not have the same roles. In brief, the Father is the Planner, the Son is the Accomplisher, and the Holy Spirit is the Applier of salvation to believers.
What scripture plainly teaches is that God has one and only one essence (nature) and that it is not contradictory to have three persons in one essence.
All members of the Trinity are equal in essence, but they do not have the same roles. It is a heresy (called subordinationism) to affirm that there is an ontological subordination of one member of the Trinity to another, since they are identical in essence.
Nonetheless, it is clear that there is a finctional subordination; that is, not only does each member have a different function or role, but some functions are also subordinate to others.