If you know what He has done at infinite cost to himself—He’s put you into a relationship so that you’ll never be rejected by Him—then your motivation when you sin is to go get Him. You want fellowship with Him. When the thing that most assures you is the thing that most convicts you, you’ll be okay because when you’re convicted of sin in a gospel way it drives you toward God.
Without the gospel we hate ourselves instead of our sin. Without the gospel we’re motivated through all sorts of awful fear and pride to change and it doesn’t really change our hearts; it just restrains our hearts.