At his baptism, God confirms that Jesus is the Christ, the Messiah, who will rule on David’s throne forever. We also see what kind of king he is: humble and willing to serve.
Tools and resources you need to do a word study on the Greek word for baptism: baptizō
In Acts 16, when Luke reports on the conversion of two locals, he tells us that Paul baptized their entire households. Why would Paul baptize an entire household?