Throughout the gospels, we see Jesus model, lead, teach, inspire, convict, and instruct his followers. This instruction--the command to love the Lord our God with all our heart, soul, and mind; and to love our neighbor as ourselves--comes before The Great Commission.
A commission is a formal, written warrant, granting the power to perform various acts or duties. It's the authorization to act in a prescribed manner. And those who've been commissioned have been given a charge to serve.
So what are our "marching orders"? Go. Make. Baptize. Teach.