"The Great Commission actually begins with the declaration,
“All authority in heaven and on earth has been given to me” (Matt. 28:18).
This is the rationale for everything the church is called to do and to be.
The church’s commission is indeed directed by a purpose
(“making disciples of all nations”), but it is driven by a promise."
This is just another reminder of how often we miss the idea that gospel imperatives (the things we are commanded to do) are always stated in context with gospel indicatives (what Jesus has already done).
Rick Warren's book (Purpose Driven Church) got a lot of attention, but I fear it only reinforced many of us missing the main point. Go read the Horton article for all the details.