Matthew 21:22

But whenever we are not heard when we pray, it is either because we ask something adverse to the means of our salvation; or because the perverseness of those for whom we ask hinders its being granted to them; or because the performance of our request is put off to a future time, that our desires may wax stronger, and so may have more perfect capacity for the joys they seek after.

And that thou mightest learn, that for their sakes this was done, that He might train them to feel confidence, hear what He saith afterwards. But what saith He? "Ye also shall do greater things, if ye are willing to believe and to be confident in prayer." Seest thou that all is done for their sake, so that they might not be afraid and tremble at plots against them? Wherefore He saith this a second time also, to make them cleave to prayer and faith. For not this only shall ye do, but also shall remove mountains; and many more things shall ye do, being confident in faith and prayer.

The Gentile dogs bark against us, affirming that the Apostles had not faith, because they were not able to remove mountains. To whom we answer, that many wonders were done by the Lord which are not written; and therefore we believe the Apostles to have done some not written; and that they were therefore not written, that the unbelieving might not have in them larger room for cavilling. For let us ask them, do they believe the miracles which are written, or do they not? And when they look incredulous, we can then establish that they who believe not the lesser would not have believed the greater.