Biblical Musings 2

Sculpture at Mensa Christi. Peter Told to Feed Christ's Sheep

And Jesus came and spoke to them, saying, "All authority has been given to Me in heaven and on earth. Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things that I have commanded you; and lo, I am with you always, even to the end of the age." Amen.
Matthew 28:18-20 (NKJ)

What is involved in this command? Who is expected to carry it out and why?