The expression "Great Commission" is commonly used to refer to a special directive Christ gave in a post-resurrection appearance before he ascended back into heaven.
The "commission" is found in three complementary forms (Mt 28:18-20; Mk. 16:15-16; Lk. 24:47-27). A harmony of its elements reveals the following factors.
The followers of Christ must preach the basic components of the gospel, namely the facts about the identity of Jesus and his mission.
Their field of operation is to be worldwide, and the scope of the message is universal (i.e., to all men).
Obligations imposed upon those who hear the message are to believe it, repent of sin, and be immersed in water.
The resulting blessings are salvation from sin, possession by, and intimate fellowship with the Godhead -- Father, Son, and Holy Spirit.
While not historically parallel, John 3:3-5 (the new birth instruction) complements the "commission" passages.