Psalms 103:11

For as the heaven is high above the earth - See the notes at Psalms 57:10. Compare the notes at Isaiah 55:9. The literal translation of the phrase here would be, “For like the height of the heavens above the earth.” The heavens - the starry heavens - are the highest objects of which we have any knowledge; and hence, the comparison is used to denote the great mercy of God - meaning that it is as great as can be conceived; that there is nothing beyond it; that we cannot imagine that it could be greater - as we can imagine nothing higher than the heavens.

So great is his mercy toward them that fear him - To those who reverence and serve him. That is, His mercy is thus great in forgiving their offences; in imparting grace; in giving them support and consolation.