Baptism is an outward expression of what is taking place on the inside of a person who is putting their whole hope and trust in Jesus. It is our public declaration that our old life is over and our new life in Jesus Christ is beginning. Being immersed completely in water symbolizes a few things. It represents our being fully identified with Jesus. The word the bible uses for baptism is the same word that is used to describe dying cloth. It means to submerge cloth in the dye of a different color until every square inch of the cloth has absorbed the new color. The cloth is no longer the color it was, it is now a new color, fresh and clean. In a similar way, going under the water symbolizes that no part of us is left untouched by Jesus, all of us, every part, is being made new, fresh, and clean.
Baptism also symbolizes our identification with the death and resurrection of Jesus. Jesus died for our sins and was buried underground. We who have been previously ruled by sin are immersed in water. Jesus conquered sin and death when he rose from the dead. We are raised out of the water into a new life, one not ruled by sin or fears of death. When we baptize people we say "You being buried with Jesus in baptism unto death" and at which point we immerse the person briefly in water then quickly raise them up saying "are raised to walk in the newness of life!" and the crowd goes wild! We're not exaggerating that last part, people actually go crazy at our church. Rightly so, we are celebrating one of the most meaningful things in our faith...someone giving everything to follow Jesus. That is something to get excited about.