This is a fantastic verse!
Thomas, after years of clumsily wandering around the truth that was right there - not just in his midst, but with him most days and nights... Jesus talking, sharing, teaching, reading perhaps and retelling stories of ages past and adding a new dimension that pointed to ages future.
The man Jesus, the son of God, had called Thomas to be one of the 12! Thomas, like all of us, answered the call, the invitation, to be with Jesus, to trust him, to believe him, to follow him to some amazing, and, some dark, dark places - like us, he had no concept of what his 'yes' would entail or lead to - what it would do to his life - forever on.
Jesus tried to explain - again and again, in many ways, but they all had huge gaps in their understanding and belief. (remember they went fishing after Jesus died, as that was one of the only things they knew was true right then in their confused and troubled state John 21:3)
Jesus told them these truths - they heard the words, but knew not yet what they meant;
Do not let your heart be troubled; believe in God, believe also in me. John 14:1
v5 Thomas said to Him, “Lord, we do not know where you are going, how do we know the way?” 6 Jesus said to him, “I am the way, and the truth, and the life; no one comes to the Father but through me.
v7 If you had known me, you would have known my Father also; from now on you know Him, and have seen Him
v10 The words that I say to you I do not speak on my own initiative, but the Father abiding in me does His works
16:17 A little while, and you will not see me; and again a little while, and you will see me
v32 I am not alone, because the Father is with me
20:24 "But Thomas,...said to them, “Unless I see in his hands the imprint of the nails, and put my finger into the place of the nails, and put my hand into his side, I will not believe.”
No one has seen the Father. But in Jesus, who is the image, the likeness, the form of the Father, they started to understand who God was - in Jesus, they got to KNOW God by knowing Jesus. From John 14:7, to 'see', means to know - to understand, to believe, to trust! Not see with the eyes - but know with the heart and soul - to sense the same spirit from God, in Jesus and also in them!
When Jesus came back in his ascended state with a new spirit life (1 Pet 3:18) - now the pieces started to fit, the words make more sense! This Jesus, who said he was the son of God (wow!), who said he and the Father were ONE! (not one substance or something, but one in purpose and spirit John 17:11,22) And Jesus said they should be 'one with him' as he was with the Father.
When Thomas saw Jesus resurrected, he saw in him God the Father - as 'the one’ that they are in purpose, power, love and glory. No, Thomas didn’t literally see God, he saw Jesus who had always been showing them the Father. He now understood the depth and significance of what Jesus had been telling them. Thomas was fully grasping for the first time that the Father God was IN Jesus and not that Jesus WAS God.
God was in Christ reconciling the world to Himself 2Cor 5:19
And echoing Job,
My ears had heard of you but now my eyes have seen you. Job 42:5
Thomas saw His God in Christ Jesus - just as Jesus had been telling them.
John 14:4 And you know the way where I am going.” Thomas said to Him, “Lord, we do not know where You are going, how do we know the way?” Jesus said to him, “I am the way, and the truth, and the life; no one comes to the Father but through Me.
Clearly we would understand that Thomas knew from Jesus' words, and from his own understanding, that his God and Jesus were not the same person. Jesus is speaking to Thomas specifically. Thomas already expressed doubt in Jesus' words (John 20:25) unless I put my fingers in his hand etc.
Thomas is being prepared for his awakening when Jesus is raised from the dead and Thomas finally gets it. Did Thomas think Jesus raised himself? That's not what Jesus had been teaching them. John 11:23-
As if Thomas would expect his GOD to have nail holes in his hands! Let alone die on a cross and be dead for 3 days!
From this scriptural basis, carefully preserved for us, we can readily see the truth and not have to draw impulsive conclusions from one verse alone.
Thomas addressed two persons - His Lord Jesus, and through Jesus, his God Yahweh.
We can of course take these words and misunderstand what Thomas meant. We might construe it to mean Jesus IS God - as many have done. But to do so is to ignore the repetitive and consistent statements from Jesus who said that he was;
'a man who has told you the truth that I heard from God' John 8:40
who could do nothing of himself - no words, no miracles, unless the Father did it through him.
a Lamb sent to die (and was raised by his Father and God)
exalted to the heavens to be with the Father (appointed heir of all things Heb 1:2)
We can ignore the statements from the Apostles about Jesus having a God;
1 Pet 1:3 Praise be to the God and Father of our Lord Jesus Christ (Rom 1:7, Eph 1:3, Col 1:3, 2 Cor 1:3, 11:31, Rom 15:6, Acts 2:36
Phil 2:9 Therefore God exalted him to the highest place and gave him the name above all names
John 20:17 I ascend to my Father and your Father, and my God and your God.
who clearly understood and taught that Jesus was certainly NOT God, but the glorious son OF God.
Or we can stick to a few other verses that seem to say Jesus IS God when we read things into the Word of God that are not supported by the broad and consistent narrative.
Even when Jesus is ascended at God's right hand, he still refers to God as 'my God', Rev 1:5-6, 3:2, 12.