Albert Barnes Commentary Psalms 121:4

"Behold, he that keepeth Israel Will neither slumber nor sleep." — Psalms 121:4 (ASV)

Behold, he that keepeth Israel - The Keeper - the Guardian - of his people. The psalmist here passes from his own particular case to a general truth - a truth to him full of consolation. It is, that the people of God must always be safe; that their great Guardian never slumbers; and that he, as one of his people, might, therefore, confidently look for his protecting care.

Shall neither slumber nor sleep - Never slumbers, never ceases to be watchful. Man sleeps; a sentinel may slumber on his post, by inattention, by long-continued wakefulness, or by weariness; a pilot may slumber at the helm; even a mother may fall asleep by the side of the sick child; but God is never exhausted, is never weary, is never inattentive. He never closes his eyes on the condition of his people, on the needs of the world.