We know that the 1st century use of the word, "God" was broader than it is used today and was sometimes meant in a lesser sense. So, we must endeavor to ascertain whether or not John meant to show that Jesus was God Himself, that is, YHWH.
 

First of all, we have John's clear statement of what, exactly, he is trying to convince us of - the REASON he wrote his gospel, and it's NOT to convince us that Jesus is YHWH Himself.

 

John 20: 30, 31: Now Jesus did many other signs in the presence of the disciples, which are not written in this book; but these are written that you may believe that Jesus is the Christ, the Son of God, and that believing you may have life in his name.

 

John's purpose is to convince us that Jesus is the Christ, that is, the Messiah, the Son of God - not God Himself.

 

In spite of this, can we demonstrate that John thought of Jesus as God? Consider these statements:

 

• John 17:3: Now this is eternal life: that they may know you, the only true God, and Jesus Christ, whom you have sent.

• John 20:17: But go to my brothers and tell them, 'I am going to my Father and your Father, to my God and your God.'

• John 1:18: No one has ever seen God; the only Son, who is in the bosom of the Father, he has made him known.

• John 3:17: For God sent the Son into the world, not to condemn the world, but that the world might be saved through him.

• John 3:34, 35: For he whom God has sent utters the words of God, for it is not by measure that he gives the Spirit; the Father loves the Son, and has given all things into his hand.

• John 5:30-32: I can do nothing on my own authority; as I hear, I judge, and my judgment is just, because I seek not my own will but the will of him who sent me. If I bear witness to myself, my testimony is not true; there is another who bears witness to me, and I know that the testimony which he bears to me is true.

• 8:17, 18: "In your law it is written that the testimony of two men is true; I bear witness to myself, and the Father who sent me bears witness to me."

• 8:40: "...but now you seek to kill me, a man who has told you the truth which I heard from God; this is not what Abraham did."​

 

This is but a small percentage of the passages in John's Gospel that could be brought to bear that show the distinction that John makes between Jesus and God. John does not conceive of Jesus being God. He conceives of Jesus being God's Son, the Messiah, the King of Israel.

 

• John 1:49: "Rabbi, you are the Son of God! You are the King of Israel!"

• See: Verily, verily, I say unto you, Before Abraham was, I am. (John 8:58).

And also:

• I am the Alpha and the Omega, saith the Lord God, who is and who was and who is to come,  the Almighty. (Rev 1:8)

 

Both of these pages deal with John's categories of thought and language. 

 

So, I find it hard to believe that John would write all the above, and more that I didn't include for the sake of brevity, and then turn around and give us this episode with the understanding that Thomas was calling Jesus, GOD, that is, YHWH. Thomas must have meant, "god" not, GOD.

 

The capitalization on the word "God" is the prerogative of the translator. In the Greek there is no distinction, it's either all caps or all lower case. The translators are, as far as I know, Trinitarians, and therefore their theological bias is responsible for the capitalization of the word, "God."

 

That the word, "God/god/gods" had a much broader use in the ancient Semitic world is easily demonstrable.

 

The Hebrew word in each of the following is "elohim" = god or gods. To what, exactly, the word, "elohim" refers to is determined by the context. So the translators will render "elohim" as God, god or gods, judge or judges, ruler or rulers, master, etc. based on the context.

 

• Ps 82:1: A Psalm of Asaph. God has taken his place in the divine council; in the midst of the gods (elohim) he holds judgment:

• Ps 82:6: I say, "You are gods (elohim), sons of the Most High, all of you;

• In John 10:34-36 Jesus says that the "gods" in this passage are the people to which the word of God came. That the "elohim" in this passage are not YHWH or GOD is clear. YHWH is designated by, "the Most High."

• Exodus 4:16: He shall speak for you to the people; and he shall be a mouth for you, and you shall be to him as God (elohim).

• Exodus 7:1:  And the LORD said to Moses, "See, I make you as God (elohim) to Pharaoh; and Aaron your brother shall be your prophet." Moses is here designated "elohim" - god.

• Exodus 22:28: You shall not revile God (elohim), nor curse a ruler (elohim) of your people

• Exodus 21:6: then his master (elohim) shall bring him to God, and he shall bring him to the door or the doorpost; and his master (elohim) shall bore his ear through with an awl; and he shall serve him for life. The slave has a god - his master.

• 1 Samuel 2:25: If one man sin against another, the judge (elohim) shall judge him: but if a man sin against the LORD, who shall entreat for him?

 

A judge is called "god". In English we would say that the judge is like God as far as his office to administrate justice. The Hebrews didn't have the word, "judge" - they used the word, "god."

 

• Psalm 97:7: All worshipers of images are put to shame, who make their boast in worthless idols; all gods (elohim) bow down before him.

• Psalm 45:6, 7: Thy throne, O God, is for ever and ever: the scepter of thy kingdom is a right scepter. Thou lovest righteousness, and hatest wickedness: therefore God, thy God, hath anointed thee with the oil of gladness above thy fellows.

 

Hebrews 1:8,9: But of the Son he says, "Thy throne, O God, is for ever and ever, the righteous scepter is the scepter of thy kingdom. Thou hast loved righteousness and hated lawlessness; therefore God, thy God, has anointed thee with the oil of gladness beyond thy comrades."
 

The fact that the word "God" is used in the secondary sense as a representative of God in Hebrews 1:8 is shown by the next verse. In Hebrews 1:9 the one true supreme God is described as the Son's God. "Thou hast loved righteousness, and hated iniquity; therefore God, even thy God, hath anointed thee with the oil of gladness above thy fellows." (Hebrews 1:8, 9 is a quotation of Psalm 45:6, 7.) If the Son has a God, then he is not that God.
 

As noted above on Psalm 82:6, in John 10:34-35 it says, "Does it not stand written in your Law," replied Jesus, "`I said, you are gods'? If those to whom God's word was addressed are called gods (and the Scripture cannot be annulled)..."
 

Here Jesus says God himself has called certain people "gods" - and appeals to Scripture for authority.

 

In I Corinthians 8:5-6 Paul says, "For if so-called gods do exist, either in Heaven or on earth--and in fact there are many such gods and many such lords--yet we have but one God, the Father, who is the source of all things and for whose service we exist, and but one Lord, Jesus Christ, through whom we and all things exist" (Weymouth translation).
 

So we see that when an ancient Jew called someone, "god" as in Thomas exclaiming, "My Lord and my God!" it doesn't necessarily mean that Thomas was saying that by his use of the word, "God" that he meant YHWH. What is meant must be determined by the context, and the context of John's Gospel shows us that John's purpose is to show that Jesus is the Messiah, the Son of God, NOT God.