Why does baptism matter? Baptism as we know it has not always been done in the Bible. In fact, until John the Baptist, no one baptized another. Ritual cleansing was done to rid yourself of everyday sins and situations that could make a person unclean and unfit for worship. It was not just sin that made one unclean in the OT. A whole list of ordinary life events could make one unclean, and thus in need of a ritual cleansing before approaching God in worship. Improper diet, a woman's monthly cycle, contact with a dead body...the list goes on. And to approach God, you had to go through a cleansing bath every time.
All over Israel archaeologists have unearthed cleansing pools. In Hebrew a cleansing pool is called a mikveh (pronounced mic va). Mikvehs are found on the temple mount in Jerusalem. But unlike baptism where someone administers the immersion, in the OT this washing in the mikveh was a self-cleansing. It had to be repeated every time you became unclean. You had to wash in the mikveh before every occasion you worshiped or presented a sacrifice. But when John the Baptist showed up all that was over. He proclaimed a baptism of repentance and forgiveness and he baptized Jesus calling him the "lamb of God who takes away the sins of the world."
So today, I have only to be baptized once. It's not to save me from my sin. That's not why Jesus was baptized. Just as Jesus laid down his life to do the will of the Father, so too I, when I was baptized, laid down my life to do the will of Jesus. My baptism shows the inward change that results in my outward and public confession that Jesus is Lord. That's the voluntary confession of the believer when she is baptized. We spend the rest of our lives living out and up to those three words: Jesus is Lord. Are you living up to your baptism?