In today’s culture we put stickers of our alma mater on the bumper of our cars, we wear shirts embroidered with the name of our employer, and more to identify us with a larger grouping of people. That’s essentially what baptism meant for people in Jesus’ day. Even though it’s a holdover from a different culture, the church throughout history has considered water baptism as one of two ordinances of the church — the other being communion.
Baptism today is publicly identifying with the person and teaching of Jesus Christ and a welcoming into the local expression of the body of Christ (the church). Jesus himself even signed up to be baptized (Mark 1:9), which is all the more reason to obey and follow his lead.