“This man was instructed in the way of the Lord; and being fervent in the spirit, he spake and taught diligently the things of the Lord, knowing only the baptism of John.”
King James Version (KJV)
18:25 This man had been instructed - Though not perfectly, in the way of the Lord - In the doctrine of Christ. Knowing only the baptism of John - Only what John taught those whom he baptized, namely, to repent and believe in a Messiah shortly to appear.
Ac 18:25 He spake and taught diligently the things of the Lord. That is, all that John understood. He believed that Jesus was the one coming after John, but he had learned only the gospel of the Lord's first commission (Mt 10:5,6). He was ignorant of the gospel of the second commission (Mt 28:19).