After His resurrection, Jesus gave them the final Gospel commission for this age, and in it He commanded baptism as an obligatory ordinance for this Gospel dispensation:
The Gospel was the message He brought and preached—the Good News of the government of God. It is necessary to believe the Gospel to receive salvation. The government (or Kingdom) of God is a kingdom of laws. There can be no government without law. It is "he that is baptized" that will be saved. It is part of the divine commission—a required ordinance for salvation!