Ever downplay a mistake or a sin? Ever speak of it as if it wasn’t that bad or even worth mentioning? Ever make excuses for it? Ever deny that you sin?
“If we acknowledge [grant, concede, accept, admit, recognize, confess] our sins, he is faithful and just, that he forgive to us our sins, and cleanse us from all wickedness.”
God expects us to acknowledge that we are sinners saved by His grace. If we accept our sinful state and concede that it displeases God, then “He is faithful and just,” and forgives “us our sins.” As if that isn’t enough, He “cleanses us from all wickedness.”
He does this; we don’t. God is faithful and just. He is forgiving. And He has the power to wash us white as snow though our sins be as scarlet.