It must be noted that this is God’s ordinary means of bestowing the grace of forgiveness. A Protestant who wholeheartedly and humbly confesses his sins as he has been taught to confess (which varies greatly within Protestantism) doesn’t necessarily miss out on forgiveness. God is never bound by his own designs. At the very least, though, the Protestant does miss out on the peace that Catholics enjoy as they leave the confessional with the freedom of knowing that they have been forgiven.
