According to Chalcedonian Trinitarians, did Thomas - a devout Jew - believe God had died at John 20?

Insomuch as David said in the hundred and tenth psalm :

The Lord said unto my Lord . . . . [Psalm 110:1 KJV]

so Thomas said unto Jesus of Nazareth, who stood before him in humanity :

My Lord and my God . . . . [John 20:28 KJV].

Neither of these had to wait for 325 AD for a Council to inform them of the Ones they worshipped. They worshipped in faith.

They worshipped for they knew the Ones they worshipped. They had a knowledge, by faith, of Persons whom they knew in experience.

They both knew that Deity is Spirit. Deity is eternal. Deity is unchangeable. Deity neither fades nor ages nor alters nor dies. These truths are self-evident (if one has faith, but not if one denies the One True Deity.).

Nor does a perfect humanity die. It is sustained in righteousness and life.

Nor did Jesus 'die' in the sense of succumbing to natural process or violent action.

Jesus tells us himself that he gave up his spirit voluntarily :

No man taketh it from me, but I lay it down of myself. I have power to lay it down, and I have power to take it again. This commandment have I received of my Father. [John 10:18 KJV]

Thomas would have been aware of these words of Jesus of Nazareth. The words imply that Jesus possessed human nature but the words also imply that Jesus had the Divine ability (which humans do not have) to relinquish his life voluntarily, yet not by self-murder.

This was a power within him, as God, and this was a commandment received by him from God, even the Father.

Thus by these words alone (as well as an abundance of other statements by the one born of Mary in Bethlehem) Thomas would have realised (and by his statement, My Lord and my God, it is evident that he did realise) that the one standing before him, with imprinted scars in his hands and feet and side, was altogether human and altogether Divine.

There is no evidence in the text, and no evidence anywhere in other scriptures that Thomas (or any other true follower of Jesus Christ) had the notion or the concept that 'God could die'.

The idea is simply not there on the page.

Neither does anything stated at the Council of Nicea imply that 'God could die'. The notion is totally foreign to Trinitarian doctrine.

Thomas knew that the Son of God had died on a cross at Golgotha. This One was known to him and all the other disciples as Jesus Christ, who had the titles of Son of God and Son of Man.

Thomas had been missing the first time the resurrected Christ miraculously appeared amongst the other disciples in a room with a locked door. A week later, he was with them, and once more the risen Christ miraculously appeared in their midst, very much alive. Even though he bore the scars of his crucifixion, he was not ailing or in need of help. On the contrary, he was in control of everything, and Thomas did not need to be invited to acclaim the risen Christ as his Lord, and his God. He did that spontaneously, and Christ accepted that worship without a word of criticism or caution.

This event formed an important basis for much later Chalcedonic statements about the full deity of Christ. The eyewitness accounts make it clear that all of Jesus' Jewish and Gentile followers back then acclaimed Christ as God (as the rest of the New Testament goes on to show). They knew that Jesus of Nazareth had truly died, had truly been resurrected, and truly returned to heaven, from whence he would one day return. It only seems to be in later generations that people began to doubt such basic facts of the Christian faith, and so the need arose to thrash out the full deity of Christ in such a way that belief in that formed an essential part of being able to call oneself a Christian.

The answer to the question is that Thomas believed that the Son of God had died and had been resurrected, proving to his satisfaction that the risen Christ was both Lord, and God. A further question would need to be raised to thrash out the exquisite connections between the full deity of Christ, the Father, and the Holy Spirit if that is actually the understanding that is sought, for the Christian faith is clear that God the Father did not die, nor did God the Holy Spirit. But God the Son certainly died and was resurrected.

The Council of Chalcedon of A.D. 451 declares that Jesus Christ is One Person who has Two Natures:

Our Lord is truly God and truly man, of a reasonable soul and body, consubstantial with the Father according to the Godhead, and consubstantial with us according to the manhood; in all things like unto us without sin; begotten before all ages of the Father according to the Godhead, and in these latter days for us and for our salvation born of the Virgin Mary, the mother of God according to the manhood; one and the same Christ, Son, Lord, only begotten, to be acknowledged in two natures, inconfusedly, unchangeably, indivisibly, inseparably, the distinction of natures being by no means taken away by the union, but rather the property of each nature being preserved and concurring in one person and one subsistence; parted or divided into two persons but one and the same Son, and only begotten, God, the Word, the Lord Jesus Christ. Source: God the Father, God the Son, page 281 by Dr. Martyn Lloyd-Jones, Westminster Chapel, London, England.

One person, two natures, the two natures unmixed, joined but not mixed, not fused, not intermingled, remaining separate, God and man. In Reformed doctrine, the divine nature and the human nature are united in the person of Christ.

The Council of Chalcedon anathematized those who taught that Christ had only a single, divine nature and those who taught a “mixture” of His two natures. The “Chalcedonian Definition” affirms that Christ is “the same perfect in Godhead and also perfect in manhood; truly God and truly man.” He is “consubstantial [h*m*ousios] with the Father according to the Godhead, and consubstantial with us according to the Manhood.”

By affirming that Jesus Christ is one Person who is both divine and human, the Council of Chalcedon made it easier to identify error. The Chalcedonian Definition affirms the truth that Jesus Christ is fully divine and, at the same time, fully human. He is both the Son of God (1 John 5:10) and the Son of Man (Mark 14:21). Jesus, the Word incarnate, assumed perfect humanity in order to save fallen humanity. He could not have saved us unless he was fully God and fully man.

Jesus said his soul was exceedingly sorrowful unto death (Mark 14:34). His suffering involved the body and the soul, so He had to be a man. In order that His sacrifice might have infinite value, He had to be God as well as man.

Paul says had they known it, they would not have crucified “the Lord of glory” (1 Corinthians 2:8). You cannot crucify God (who is Spirit) but the body of Jesus could be crucified. Yet Paul does not say that His body was crucified. Paul says they crucified “the Lord of glory”. In other words, what happens in the one nature or the other is ascribed to the one person.

When Thomas fell down and declared that the risen and resurrected Christ was his Lord and his God, he was acknowledging him as both Lord and God. Be assured that Thomas was not worshipping two Gods. He acknowledged the reality of Jesus’ divine nature whilst also holding to the monotheistic doctrine that there is only One God.

You ask if Thomas “believed God could have and did die”. If by “death” you mean “a cessation of existence,” then, no, God did not die. Neither the Father nor the Son nor the Holy Spirit will ever cease to exist. The Son left the body He temporarily inhabited on Earth, but His divine nature did not die, nor could it. Thomas was neither a Unitarian nor a follower of Arianism.

To conclude: The Logos, the Son of God, the Christ, became man that the children of men might become children of God. Thomas finally saw the light (spiritually speaking) when he fell down on his knees and cried out in reverent worship, “My Lord and my God.”