It is enough for us to be persuaded that our supplication will be welcome when we address our requests to Him, since His grace has opened the way. Moreover, prayer always bears fruit. But we do not know exactly how, and since it is beyond our senses, we must wait with patience, and yet always persevering in our prayers.

…Thus, let us learn to pray to God in all our extremity, and even when it seems that nothing else can be done, let us keep on, nevertheless… let us consider what He has commanded us to do: that is, to wait in patience and humility for whatever the outcome will be. Although we are like poor blind men – certainly so – we ought to be satisfied by this clear teaching given to us; namely, that God does care for us, even when He seems to have turned His back on us.

John Calvin, Sermons on 2 Samuel, pg 588.