Jesus commanded all who believe in Him to be baptised in the Name of the Father, Son, and Holy Spirit. Baptism does not save a person or erase original sin. This can only by done by grace through faith in the finished work of Jesus Christ on the cross. Once a person has been saved by grace through faith, baptism is an act of obedience and is, itself, a symbol of one's union with Jesus in death (going under the water) and resurrection (coming out of the water).
Baptism has ancient biblical roots that go back to Noah and Moses. Just as Noah was baptized through the flood of God's judgment, so also those who are baptized into Christ will come through God's Final Judgment. Just as Israel was baptized through the Red Sea as they came out of slavery in Egypt, so also those who are baptized into Christ have been freed from slavery to sin.
Sermons on Baptism