"And He [Christ] Himself is the propitiation for our sins . . . "
"Propitiation" means atonement, sacrifice, satisfaction. Jesus Christ Himself, plus nothing, is the "propitiation" for the sins of all God's elect, who will be saved in time and space. Our works are not our propitiation. Our efforts are not. Our "working together with God" is not.
Christ *alone*, Himself satisfies God's wrath against sin; and He (Jesus) bore the punishment for the redeemed. Therefore, let us destroy all false and God-dishonoring "gospels" of works, and let us rejoice in the fact that we have a real and blessed Savior.
[Puritan quote of the day: "[God] gave His only begotten Son to be a propitiation for our sin, and accepted His suffering instead of ours." --John Shower, in "God's Thoughts and Ways are Above ours"]