“O Lord my God, I cried to you for help, and you have healed me.” -Psalm 30:2
Answers to prayer such as David experienced are faith building. Apparently, David was on the verge of death and directed his supplications solely to the Lord, who heard him and healed him. David knew he had not prayed in vain.
John Calvin noted on this passage that, “When God hears our prayers, it is a proof which enables us to conclude with certainty that he is the author of our salvation, and of the deliverance which we obtain.”
The Apostle John reminded the early church of this very same truth when he wrote,
“I write these things to you who believe in the name of the Son of God, that you may know that you have eternal life. And this is the confidence that we have toward him, that if we ask anything according to his will he hears us. And if we know that he hears us in whatever we ask, we know that we have the requests that we have asked of him.” -1 John 5:13–15