"Let us consider how to stir up one another to love and good works, not neglecting to meet together, as is the habit of some, but encouraging one another..." I think that's referring to Sunday's assembly and more.

The New Testament records how Christians were meeting up to hang out daily (Acts 2:46), and often focuses on us having the right relationships: family, friendship, and partnership with each other, and loving, caring ambassadorship to the world, who we fight to rescue from Satan. 

Every day we have chances to assemble with two groups of people: Christians, or those who aren't. Who do you assemble with most? The more we assemble with those who stir us up to love and good works, and who encourage us in Christ, the better we'll be as ambassadors and warriors for Christ.