On the day I called, you answered me;
my strength of soul you increased.
David's experience with answered prayer was that God heard him when he offered praise as he called out to the Lord with his troubles. In fact, God answered David's prayers the same day that David cried out. God was timely and true in His care.
The result of such answered prayer was personal strength and encouragement for David. God strengthened the king's heart by the immediate show of care. Prayer was a strength-building exercise. It increased David's trust in God and it gave him even more occasion to praise and worship the LORD. God's care was not lacking. God showed Himself strong and loving and David was grateful and worshipful.
Some of my prayers have now been years in the praying. I do carry burdens to You. Yet your mercies are new every morning so that I always have answered prayer and reason for praise, even as some of my prayers still reside with Your sovereign wisdom and timing. You strengthen my heart with Your care and always plentiful daily provision. I am encouraged by David's grateful praise to keep trusting You. I thank You and I worship You.