Albert Barnes Commentary Psalms 33:18

"Behold, the eye of Jehovah is upon them that fear him, Upon them that hope in his lovingkindness;" — Psalms 33:18 (ASV)

Behold, the eye of the Lord is upon those who fear him - He watches over them, and he guards them from danger. His eye is, in fact, upon all people; but it is directed with special attention to those who fear him and trust in him. Their security is in the fact that the eye of God is upon them; that he knows their needs; that he sees their dangers; and that he has ample ability to deliver and save them.

Upon those who hope in his mercy - Upon the pious; upon his friends. The expression is a very beautiful one. It describes the true state of a pious heart; it in fact characterizes the whole of religion, for we imply all that constitutes religion on earth when we say of a man that—conscious of his weakness and sinfulness—he hopes in the mercy of God.