First, the quotes by John Calvin (all taken from his Institutes of the Christian Religion):
From the previous part of the work we clearly see how completely destitute man is of all good, how devoid of every means of procuring his own salvation.And now Jonathan Edwards:
To know God as the sovereign disposer of all good, inviting us to present our requests, and yet not to approach or ask of him...[would be] just as if one told of a treasure were to allow it to remain buried in the ground. Hence the Apostle, to show that a faith unaccompanied with prayer to God cannot be genuine, states this to be the order: As faith springs from the Gospel, so by faith our hearts are framed to call upon the name of God (Rom. 10:14). And this is the very thing which he had expressed some time before—viz. that the Spirit of adoption, which seals the testimony of the Gospel on our hearts, gives us courage to make our requests known unto God, calls forth groanings which cannot be uttered, and enables us to cry, Abba, Father (Rom. 8:26).
To prayer, then, are we indebted for penetrating to those riches which are treasured up for us with our heavenly Father...Accordingly, we see that nothing is set before us as an object of expectation from the Lord which we are not enjoined to ask of Him in prayer, so true it is that prayer digs up those treasures which the Gospel of our Lord discovers to the eye of faith...Hence, admirable peace and tranquillity are given to our consciences; for the straits by which we were pressed being laid before the Lord, we rest fully satisfied with the assurance that none of our evils are unknown to him, and that he is both able and willing to make the best provision for us.
As God in his word enjoins common prayer, so public temples are the places destined for the performance of them...we must, on the other hand, beware of imitating the practice which commenced some centuries ago, of imagining that churches are the proper dwellings of God, where he is more ready to listen to us, or of attaching to them some kind of secret sanctity, which makes prayer there more holy. For seeing we are the true temples of God, we must pray in ourselves if we would invoke God in his holy temple. Let us leave such gross ideas to the Jews or the heathen, knowing that we have a command to pray without distinction of place, “in spirit and in truth,” (John 4:23).
...it would not be reasonable to suppose, that merely such a circumstance, as many people praying at the same time, will directly have any prevalence with God... [source]
By our constancy in prayer, we cannot be profitable to God; and if we leave it off, God will sustain no damage: he doth not need our prayers... [source]