While Apollos was at Corinth, Paul passed through the interior and came to Ephesus. There he found some disciples and asked them “Did you receive the Holy Spirit when you became believers?” “No,” they answered, “we have not even heard that there is a Holy Spirit.” Acts 19:1-2
This is an arena where I’m going to do more digging during the next couple of years. The issue surrounds the transition from the Torah teaching where God’s Spirit is mentioned constantly to the later development of the Talmud where we have a unitary version of God. No Spirit. And certainly no Son.
Something happened in between. The teaching of the Spirit was lost. Somehow, somewhere along the way God became a unitary being in Jewish theology.
What we do know is that ideas develop over a long period of time. The Talmud was not developed in a vacuum. Those ideas had a history behind them. That seems to be hinted at in Acts 19. A similar situation occurred with the development of Gnosticism. While it did not become a formal religion for a couple centuries after the NT documents were composed one can see the ideas as they were formed and competed with Judaism and Christianity, most notably in the writings of John. John is an apologetic for Judeo-Christian thought against theological Platonism, what would become formal Gnosticism.
What happened in Jewish theology is one question. Why was the teaching of God’s spirit lost? How was it lost? All this transpired before Jesus’ time. Christianity is not to blame for this.
Of note here is the content of the apostolic message. It reads as though there is a recognition of this problem and a sequential evangelistic apologetic to bring Jewish people to the Messiah. They didn’t pursue trying to prove that the Spirit existed. In this instance Paul brought the disciples from the teachings of John to the presence of Jesus as Lord. The spoke in tongues and prophesied in the synagogue, a consistent use of the Spirit as outlined in I Corinthians.
Now the Spirit was present and that led to Jesus.
It’s almost like a sequential approach to evangelism. The disciple, being Jewish, was moved from a unitary view of God to a binitarian view (“bi” = two, God and the Holy Spirit) and then to a trinitarian view (“tri” = three, God, the Spirit, and the Son). Though our formal syllogism of God = Father/Son/Spirit was not at play the principle of God having both a Spirit and a Son seems quite clear. It seems to be an evangelistic use of the Trinity. It’s done without argumentation but instead with presentation.