1 John 5:15

And if we know (for a fact, as indeed we do) that He hears and listens to us in whatever we ask, we know (with settled and absolute knowledge) that we have (granted to us) the request which we have asked from Him. 

John knew for a fact that God listens and hears the prayers. Our confidence in God’s faithfulness and love should increase so that we can attend to our needs as we pray to God. When we use our faith in prayer, God will answer our requests.