John was involved in a Jewish practice that was a baptism of repentance. One did not receive entrance into the NT family of God, and one did not receive the Holy Spirit when receiving John’s baptism. Trinitarian baptism was introduced by Jesus and was made mandatory when he told the disciples after he had risen from the dead that “All authority in heaven and on earth has been given to me. Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you; and lo, I am with you always, to the close of the age.” [Matt 28:18-20]
This contrast becomes even more clear in the Book of Acts when Paul meets some of John’s disciples. The following passage is quite instructive:
Acts 19:1-7
“WHILE APOLLOS was at Corinth, Paul passed through the upper country and came to Ephesus. There he found some disciples. And he said to them, “Did you receive the Holy Spirit when you believed?” And they said, “No, we have never even heard that there is a Holy Spirit.” And he said, “Into what then were you baptized?” They said, “Into John’s baptism.” And Paul said, “John baptized with the baptism of repentance, telling the people to believe in the one who was to come after him, that is, Jesus.” On hearing this, they were baptized in the name of the Lord Jesus. And when Paul had laid his hands upon them, the Holy Spirit came on them; and they spoke with tongues and prophesied. There were about twelve of them in all.”
I hope this helps.