John preached that Jesus was the Son of God. At Jesus baptism, the Father and the Spirit made that plain too.
BibleGateway: Luke 3:15-18, 21-22 ESV Text: Luke 3:15-18, 21-22 Luke 3:15–18 (Listen) 15 As the people were in expectation, and all were questioning in their hearts concerning John, whether he might be the Christ, 16 John answered them all, saying, “I baptize you with water, but he who is mightier than I is coming, the strap of whose sandals I am not worthy to untie. He will baptize you with the Holy Spirit and fire. 17 His winnowing fork is in his hand,…