Charles H. Spurgeon on Psalms 121:8

The Lord shall preserve thy going out and thy coming in. All actions being comprehended under one of these two sorts, "going out" to more public, and "coming in" to more private affairs; or again, "going out" to begin, and "coming in" at the end of the work. But by this expression may here perhaps be more particularly signified that God would protect David, even to the end of his days, whenever he marched out with his armies, or brought them home. —Thomas Fenton.