6 Well now: I have already told you, my, beloved brethren, let no man turn toward us. For what are we? Or what are you? What, but the Church of God which is known to all? And, if it please Him, in that Church are we; and those of us who by love abide in it, there let us persevere, if we would show the love we have. But then the apostle Paul, what evil are we to think of him? He not love the brethren! He not have within himself the testimony of his conscience in the sight of God!
Paul not have within him that root of charity whence all good fruits proceeded! What madman would say this? Well then: where find we that the apostle asked and did not receive? He says himself: “Lest I should be exalted above measure through the abundance of the revelations, there was given to me a thorn in the flesh, an angel of Satan to buffet me. For which thing I besought the Lord thrice, that He would take it from me. And He said unto me, My grace is sufficient for you: for strength is made perfect in weakness.” Lo, he was not heard in his prayer that the “angel of Satan” should be taken from him.
But wherefore? Because it was not good for him. He was heard, then, for salvation, when he was not heard according to his wish. Know, my beloved, a great mystery: which we urge upon your consideration on purpose that it may not slip from you in your temptations. The saints are in all things heard unto salvation: they are always heard in that which respects their eternal salvation; it is this that they desire: because in regard of this, their prayers are always heard.
Source: Homilies on the First Epistle of John (New Advent)