John 20:28 "My Lord and my God."
God" means a strong one. Christ is called "The mighty God" at Isaiah 9:6, "a god" at John 1:1 (NW, see here), and "the only-begotten god" at John 1:18 (NW). Jehovah is not the only god or strong one. The very fact that he is called the Almighty God indicates that there are other gods not so mighty, not almighty like him. So Thomas could call Jesus God, but not THE God, and three verses later Jesus is called "the Son of God," as we read (NW): "But these have been written down that you may believe that Jesus is the Christ the Son of God, and that, because of believing, you may have life by means of his name." Joh 20:29-31 So there was no objection to John's reporting that Thomas addressed Jesus as a deity, and certainly John does not say that Thomas' address to Jesus was to make us believe that Jesus was The God, but says it was to make us believe Jesus was God's Son. In this same chapter (Joh 20:17, NW) Jesus said: "I am ascending to my Father and your Father and to my God and your God." He was not ascending to himself. But now you will say Thomas used the Greek definite article "the" (ho) before "God," proving he called Jesus The God.[see * below, NWT Defense editors] The article "the" is in the nominative case in the Greek, but the word "God" here is in the vocative case and of such A. T. Robertson says in his A Grammar of the Greek New Testament in the Light of Historical Research, on page 461: "The article with the vocative in address was the usual Hebrew and Aramaic idiom, as indeed in Aristophanes we have HO PAIS AKOLOUTHEI. It is good Greek and good Aramaic too when we have ABBA HO PATER (Mark 14:36) whether Jesus said one or both. In Matthew 11:26 (nai, ho patér) we have the vocative. When the article is used, of course the nominative form must occur. Thus in Rev. 18:20 we have both together, OURANE KAI HOI HAGIOI. Indeed the second member of the address is always in the nominative form. Thus KYRIE, HO QEOS, HO PANTOKRATOR (Rev. 15:3). Compare John 20:28." Page 462: "When Thomas said HO KYRIOS MOU KAI HO QEOS MOU (John 20:28), he gave Christ full acceptance of his deity and of the fact of his resurrection." Page 466: "In John 20:28 Thomas addresses Jesus as HO KYRIOS MOU KAI HO QEOS, the vocative like those above. Yet, strange to say, Winer calls this exclamation rather than address, apparently to avoid the conclusion that Thomas was satisfied as to the deity of Jesus by his appearance to him after the resurrection. Dr. E. A. Abbott follows suit also in an extended argument to show that KYRIE HO QEOS LXX way of addressing God, not HO KYRIOS KAI HO QEOS. But after he had written he appends a note to p. 95 to the effect that 'this is not quite satisfactory. For [John] 13:13 PHONEITE ME HO DIDASKALOS KAI HO KYRIOS, and Rev. 4:11 AXIOS EI, HO KYRIOS KAI HO QEOS HEMON, ought to have been mentioned above.' This is a manly retraction, and he adds: 'John may have used it here exceptionally.' Leave out 'exceptionally' and the conclusion is just. If Thomas used Aramaic he certainly used the article. It is no more exceptional in John 20:28 than in Rev. 4:11." So, since the use of the definite article was made before the form of address to anybody, Thomas' use of the definite article does not force his use of God to mean The God, Jehovah. Jehovah was not begotten, but existed without beginning. But according to John 1:18 (NW) Christ was the only god or strong one directly begotten or created by Jehovah, however. So Jehovah is The God; Jesus Christ is one of many who are called gods. Satan is called "the god of this system of things," Moses was said to be as god to Pharaoh, and in the Psalms men are called gods, and Jesus referred to this and argued that hence the Jews should not say he blasphemed when he said he was God's Son. And the apostle Paul said there are many called gods. But to argue that these many different ones called gods are, by virtue of this fact, The God Jehovah would be absurd. Similarly, it is absurd to try to argue that Thomas' reference to Jesus as god proves Jesus is The God, and doubly so when just three verses later Jesus is identified as God's Son.-2Cor. 4:4, NW; Ex. 7:1; Ps. 82:6; John 10:35; 1 Cor. 8:5.
From The Watchtower, 1955, September 1, "Question from Readers".
That the article with theos in John 20.28 is not 'proof' that Jesus is "God" is also shown by what we can read in Murray J. Harris' book Jesus as God, The New Testament Use of Theos in Reference to Jesus; " As for John's use of [theos] in the Fourth Gospel in reference to the pre-existent Logos(John 1.1), the incarnate Son(John 1.18), and the risen Lord(John 20.28), we should not overlook the fact that in the first two cases [theos] is anarthrous and in the third it is articular simply because a vocatival nominative followed by a possessive pronoun is invariably articular."-p.248. Italics ours.