The Israelites had committed a terrible sin. During Moses’ absence, they had forged a golden calf and had begun worshiping it. Although Moses was enraged by their idolatry, he also pled with God to spare them from the fullness of His just wrath. Because Moses was a righteous and humble man his prayer was heard and answered.
There is a twofold use of prayer: the one, to obtain strength and blessing for our own life; the other, the higher, the true glory of prayer, for which Christ has taken us into His fellowship and teaching, is intercession, where prayer is the royal power a child of God exercises in heaven on behalf of others and even of the kingdom. (Adapted from Andrew Murray, With Christ in the School of Prayer)