Baptism is the rite of admission into the Christian church in line with the Jewish rites of purification and as a symbolical representation of cleansing from the sins of which they repented. The law of Moses spoke of a water of separation, a levitical purification for sin and the entry into a new and purer life. Christian baptism represents the response of our faith of Jesus' sacrifice. It is the symbol of the fact of our faith, repentance and the gift of the Holy Ghost. This is where salvation lies and baptism confirms this.
Christian baptism is considered a symbol and a sacrament.
John's baptism of repentance included the metanoia which means a change of mind. The obligation of Christian baptism rests completely on the command of Jesus at His ascension. Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost. Jesus never commanded His followers to be baptized, He command us to go out and baptize His followers. In Acts there is no trace of one set of people only to baptize.