"...who forgiveth all thine iniquities."
Over ninety years ago Mark Guy Pearse released an exceptional book of exposition of Psalm 103 entitled "Praise: Meditations in the 103rd Psalm"
Listen to the following:
"Once when I was away among mountains, the guide said to me: "There is a wonderful echo here if you can but wake it up. Stand here with your back to this rock, and turn yourself towards that point, and now shout." I shouted. And from a hundred hollow places came the wonderful responses- far away behind me I heard it rolling in the caves and up amongst the hills; it went ringing across the lake to left of me and right of me; from away at the end of the lake it came back to me, and then away, away; whilst faint echoes of the echoes lingered in the air.
Ah, such an echo is there in the mount of the Lord if we can but wake it up. Set thy foot firm upon the promises of our God. Set thine eye upon the Crucified. Let all thy soul go forth in deepest love to Him who loved thee. And now wake up the music that sleeps on every side- "Who forgiveth all thine iniquities." All. Hark! I hear the music of it ringing away behind me, away over the chilhood, over the youth, over the years that are gone- All thine iniquities!...O, music as of heaven, I hear it ringing away to right of me and left of me, away in the dark and gloomy places of the life, away as far as all the influence of my life has gone, sweep the glad tidings- All thine iniquities!
Try it again. Once more with the faith set firmly in the promises of our God, and resting against the rock of His truth, lift thine eye to the Crucified and let thine heart adore Him. Hear it once again- "Who forgiveth ALL thine iniquities." O, blessed strains, listen! I hear it away, away for ever and for evermore, gone on to find kindred melodies in heaven itself."
Note: It must be this complete to accomplish redemption. With just one sin the Accuser could rob us of our assurance and drag us down. But thankfully "There is now no condemnation for those who are in Christ Jesus." Let this echo also forever. No Condemnation.