And now the Psalmist speaks of the greatness of God's mercy. As the heaven is high above the earth, so great is His mercy toward them that fear Him. The Psalmist also speaks of how God shows His great mercy to us, His people. As far as east is from the west, so far has He removed our transgressions from us. How beautiful and comforting this is, especially to the wretched soul that carries a heavy burden of sin and guilt.
Mercy presupposes two things.
It presupposes that you love someone and that in that love you seek the welfare of that person. This latter, after all, is the very essence of love. Whatever doesn't seek the welfare of another is not love. Mercy also presupposes that this loved one is in distress. Troubles have come upon him.