Jesus and the religious leaders often had disputes over ritual cleanliness. Jesus and his disciples didn't always seem to follow the rules about how to wash their hands before they ate. They didn't necessarily observe religious customs regarding the storage of food. Nor did they avoid people who had been deemed "unclean" by law, culture or religion.
One of the rituals to regain spiritual cleanliness was to be immersed in water. Individuals enter the waters aware of their separation from the holiness of God due to the sin in their lives, and emerge renewed, refreshed and spiritually clean.
The water truly serves as a reminder of how God is always ready to forgive when we repent of our sins.
In this tradition, but in a new way and with a new message, John immersed people in the Jordan River for the forgiveness of their sins.
He was calling the people to repentance, asking them to prepare for the kingdom of God that was coming in the person of Jesus.