Adams on Psalm 91:11

11 To keep thee in all thy ways How should those heavenly spirits bear that man in their arms, like nurses, upon earth living; or bear up his soul to heaven, like winged porters, when he dies, that refuseth the right way? They shall keep us in all our ways. Out of the way it is their charge to oppose us, as to preserve us in the way. Nor is this more a terror to the ungodly, than to the righteous a comfort. For if an angel would keep even a Balaam from sinning, how much more careful are all those glorious powers to prevent the miscarriages of God's children! From how many falls and bruises have they saved us! In how many inclinations to evil have they turned us, either by removing occasions, or by casting in secretly good motions! We sin too often, and should catch many more falls, if those holy guardians did not uphold us. Satan is ready to divert us, when we endeavour to do well; when to do ill, angels are as ready to prevent us. We are in Joshua the high priest's ease, with Satan on the one hand, on the other an angel, Zec 3:1: without this, our danger were greater than our defence, and we could neither stand nor rise.

... We have the safeguard of the empire; not only the protection of the King, from which the wicked as outlaws are secluded; but also the keeping of angels, to whom he hath given a charge over us, to keep us in all his ways. So nearly we participate of his Divine things, that we have his own guard royal to attend us.

As quoted in Spurgeon's Treasury of David.