Thy righteousness is like the great mountains; literally, like the mountains of God; and so Luther, Rosenmuller, Hengstenberg, Kay, Cheyne, and the Revised Version. According to the Hebrew idiom, this means "the very greatest mountains"—those which seem to stand the strongest and the firmest.
Thy judgments are a great deep; i.e. such as man cannot fathom—unsearchable—past finding out. O Lord, thou preservest man and beast. The providential care of God for his creatures is another of his leading characteristics, and one especially deserving man's attention and gratitude.
It is a form of his loving-kindness.