Confession of sins produces patience. The prayer of a righteous man is powerful and effective. Nothing promotes patience among Christians more than forgiveness. I can only surmise that this warring factious church to which James writes needed to clear the air. The only way they could clear the air was through confession and forgiveness.
Patience produces powerful and effective prayers.
Prayer is a powerful tool in the hands of those confessing their sins and forgiving others. Confession and forgiveness are the true signs of humble hearts bent on doing God's will on earth. In the example prayer Jesus connected seeking forgiveness and extending forgiveness as the hallmark of those seeking God. Those confessing and forgiving are the ones allowing God's will to be done on earth as it is in heaven. What an encouragement to patient endurance.