Commentaries:
Barnes' Notes
He will not suffer thy foot to be moved - He will enable you to stand firm. You are safe in his protection. Compare the notes at Psalms 38:16. This, with the remainder of the psalm, seems to be of the nature of an answer to the anxious question in Psalms 121:1 - an answer which the author of the psalm, in danger and trouble, makes to his own soul, imparting confidence to himself.
He that keepeth thee will not slumber - He will be ever watchful and wakeful. Compare Isaiah 27:3. All creatures, as far as we know, sleep; God never sleeps. Compare Psalms 139:11-12. His eyes are upon us by day, and in the darkness of the night - the night literally; and also the night of calamity, woe, and sorrow.
DISCLAIMER: Church of the Great God (CGG) provides these resources to aid the individual in studying the Bible. However, it is up to the individual to "prove all things, and hold fast to that which is good" (I Thessalonians 5:21). The content of these resources does not necessarily reflect the views of CGG. They are provided for information purposes only.