Once we grasp the equality of the three persons in the one God, one wonders why the New Testament seems to call the Father God much more than the Holy Spirit or Jesus. The issue the writers faced was to how to communicate the three persons each fully God without losing the distinctions. Especially, the many times we see the Father and the Son interacting throughout the New Testament. What the inspired writers did was primarily use God when referring to the Father and Lord when talking about the Son. The word Lord in many cases when referring to the Son would be equal to calling Jesus God.
Understanding how the New Testament uses Lord and God
Wayne Grudem writes: When we realize that the New Testament authors generally use the name “God” (Gk. theos) to refer to God the Father and the name “Lord” (Gk. kyrios) to refer to God the Son, then it is clear that there is another Trinitarian expression in 1 Corinthians 12:4–6: “Now there are varieties of gifts, but the same Spirit; and there are varieties of service, but the same Lord; and there are varieties of working, but it is the same God who inspires them all in every one.” Similarly, the last verse of 2 Corinthians is Trinitarian in its expression: “The grace of the Lord Jesus Christ and the love of God and the fellowship of the Holy Spirit be with you all” (2 Cor. 13:14). We see the three persons mentioned separately in Ephesians 4:4–6 as well: “There is one body and one Spirit, just as you were called to the one hope that belongs to your call, one Lord, one faith, one baptism, one God and Father of us all, who is above all and through all and in all.” All three persons of the Trinity are mentioned together in the opening sentence of 1 Peter: “According to the foreknowledge of God the Father, by the sanctifying work of the Spirit, that you may obey Jesus Christ and be sprinkled with his blood” (1 Peter 1:2 NASB). And in Jude 20–21, we read: “But you, beloved, build yourselves up on your most holy faith; pray in the Holy Spirit; keep yourselves in the love of God; wait for the mercy of our Lord Jesus Christ unto eternal life.”
An example of where the Father and God are interchangeable (synonymous) can be found in Matthew and Mark. I have underlined the key words.
Matthew 12:48-50 (NASB)But Jesus answered the one who was telling Him and said, “Who is My mother and who are My brothers?” 49 And stretching out His hand toward His disciples, He said, “Behold My mother and My brothers! 50 “For whoever does the will of My Father who is in heaven, he is My brother and sister and mother.”
Mark 3:33-35 (NASB)Answering them, He *said, “Who are My mother and My brothers?” 34 Looking about at those who were sitting around Him, He *said, “Behold My mother and My brothers! 35 “For whoever does the will of God, he is My brother and sister and mother.”
A second example comes from John 20:17 (NASB)“Jesus *said to her, ‘Stop clinging to Me, for I have not yet ascended to the Father; but go to My brethren and say to them, ‘I ascend to My Father and your Father, and My God and your God.'” Jesus is calling the Father his God, submitting himself to the Father. The Son took the role of taking on a human nature and giving up certain divine prerogatives. Jesus was still fully God but chose not to utilize his divine abilities (Phil. 2:5-8). As Paul writes in Philippians 2, Jesus as a human submitted himself to death, something the Father cannot do. A difference in function does not indicate inferiority of nature.
Again generally when we see the word “God” in the scriptures we can think of the Father. However, sometimes the writers used “God” when referencing Jesus or the Holy Spirit or the Triune God.
Jesus is called God in John 20:28“Thomas answered and said to Him [Jesus], ‘My Lord and my God!’” Jesus then commends Thomas for calling him Lord and God. This is a very straightforward passage identifying Jesus as God.
The Holy Spirit is called God in Acts 5:3-4 “But Peter said, ‘Ananias, why has Satan filled your heart to lie to the Holy Spirit and to keep back some of the price of the land? 4 While it remained unsold, did it not remain your own? And after it was sold, was it not under your control? Why is it that you have conceived this deed in your heart? You have not lied to men but to God.’” Lying to the Holy Spirit is lying to God because the Holy Spirit is God.
The major problem for some people is grasping the fact that Jesus was fully God and fully man. This is a huge stumbling block for Jehovah Witnesses. They cannot understand how one person can have two natures, divine and human. I will soon deal with this issue as I begin a series on Jesus as the God/man.
When we read the scriptures in context and recognize the word “God” is primarily the Father, we will clear up the passages that seem to be contradictions. The infrequent times the Son or Holy Spirit are called “God” are easily recognized by the context. We can thus acknowledge we worship one God subsisting in three persons Father, Son, and Holy Spirit; co-equal and co-eternal.
 Grudem, Wayne, Systematic Theology, Zondervan Publ., 1994, p. 230.
 There are times when the word “God” means the Trinity. Passages declaring the existence of only one God are not identifying one of the three persons but the entire Godhead (Father, Son, and Holy Spirit). James says the demons recognize the one God in James 2:19, “You believe that God is one. You do well; the demons also believe, and shudder.” Remember the Trinity teaches one God subsists in three persons.