"Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit..."
In receiving water baptism, we are following Jesus' example and obeying his command.
Water baptism is a public declaration of what Jesus Christ has done in the believer’s life, and symbolizes two powerful truths:
Jesus' own death, burial, and resurrection for our sins. The Bible says, “The wages of sin is death.” Jesus took all our sins upon Himself and died on the cross to pay the penalty for our sins. Being immersed in the water symbolizes Jesus’ death and burial, and the washing away of all our sins–past, present, and future–by his shed blood. Coming up from the water symbolizes Jesus’ resurrection, in which he overcame sin and death so that we can have eternal life in him.
The death of our "old self" to sin, and raising of our "new self" in Christ. When we're immersed in the water, we're proclaiming to heaven, earth, and hell, “My old life is gone. As Christ was buried, I am burying my old sin nature, bad habits; and past hurts, failures, and mistakes. From now on, I am dead to sin, my past, and the world’s ways.” When we come out of the water, we are proclaiming, “I am a new person with a new life in Christ Jesus.” 2 Corinthians 5:17 says, “Therefore, if anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new.”