Jesus said Thomas saw THE FATHER and he explained how. Jesus is the expression of the Father (1:18). The Father abiding in him did the works (14:9-10).

The Holy Spirit PROCEEDS FROM THE FATHER (John 15:26). Jesus breathed on them and said to them, “Receive the Holy Spirit." (John 20:22.) Because the Father was THERE in Jesus, He breathed the Spirit of God into his disciples, the Spirit which proceeds from the Father. The Father was in him and he was in the Father and that is what Thomas is confessing. He who has seen Jesus has seen the Father. Thomas confessed precisely what Jesus had taught him. When Thomas saw the risen Jesus with his wounds, he knew it was him, and he knew that if he saw Jesus, he saw the Father. And he knew this because Jesus had taught him that fact. "In that Day, you will know I am in my FATHER"........ "My Lord and my GOD."

The teachers of the Trinity are completely blind and deaf to Jesus' teaching. They cannot hear his words because they are not of God; they are not his sheep and do not hear his voice. Jesus was a teacher who gave sight to the blind; Trinitarian teachers are blind guides who lead people into darkness. But like Jesus, true believers are the light of the world (Jn 8:12; Matt 5:14). If you are born of God, testify so that the light of God in you may open their blind eyes. And pray for those who persecute you. The Spirit of Truth will guide you into all truth. In that hour, the Spirit of your Father will speak through you.

Why Trinitarian teachers do not listen to Jesus at John 14:9...

Why do you not understand what I am saying? It is because you cannot hear my word. You are of your father the devil, and you want to do the desires of your father. He was a murderer from the beginning, and does not stand in the truth because there is no truth in him. Whenever he speaks a lie, he speaks from his own nature, for he is a liar and the father of lies. But because I speak the truth, you do not believe me. Which one of you convicts me of sin? If I speak truth, why do you not believe me? He who is of God hears the words of God; for this reason you do not hear them, because you are not of God. John 5:43-47