From Andrew Murray’s The Inner Life:

God lives to love, to save, and to bless us. The believer who gives himself up to God’s service in this will find in it new life in prayer. Work for others proves the honesty of our prayer for them. Work for God reveals alike our need and our right to pray boldly. Cultivate the consciousness, and speak it before God, that you are wholly given up to His service; it will strengthen your confidence that He will hear you.