Luke 17:6

The disciples hearing our Lord discoursing of certain arduous duties, such as poverty, and avoiding offenses, entreat Him to increase their faith, that so they might be able to follow poverty, (for nothing so prompts to a life of poverty as faith and hope in the Lord,) and through faith to guard against giving offenses. Therefore it is said, And the Apostles said to the Lord, Increase our faith.

That is, that the faith which has already been received in its beginning, might go on increasing more and more to perfection.

We may indeed understand that they asked for the increase of that faith by which men believe in the things which they see not; but there is further signified a faith in things, whereby not with the words only, but the things themselves present, we believe. And this shall be, when the Wisdom of God, by whom all things were made, shall reveal Himself openly to His saints face to face.

But our Lord told them that they asked well, and that they ought to believe steadfastly, forasmuch as faith could do many things; and hence it follows, And the Lord; said, you had faith as a grain. of mustard seed, & c. Two mighty acts are here brought together in the same sentence; the transplanting of that which was rooted in the earth, and the planting thereof in the sea, (for what is ever planted in the waves?) by which two things He declares the power of faith.

He mentions the mustard seed, because, though small in size, it is mightier in power than all the others. He implies then that the least part of faith can do great things. But though the Apostles did not transplant the mulberry tree, do not you accuse them; for our Lord said not, You shall transplant, but, You shall be able to transplant. But they did not, because there was no need, seeing that they did greater things. But some one will ask, How does Christ say, that it is the least part of faith which can transplant a mulberry tree or a mountain, whereas Paul says that it is all faith which moves mountains? We must then answer, that the Apostle imputes the moving of mountains to all faith, not as though only the whole of faith could do this, but because this seemed a great thing to carnal men on account of the vastness of the body.

Or our Lord here compares perfect faith to a grain of mustard seed, because it is lowly in appearance, but fervid in heart. But mystically by the mulberry tree, (whose fruit and branches are red with a blood-red color,) is represented the Gospel of the cross, which, through the faith of the Apostles being uprooted by the word of preaching from the Jewish nation, in which it was kept as it were in the lineal stock, was removed and planted in the sea of the Gentiles.

Or this is said because faith keeps out the unclean spirit, especially since the nature of the tree falls in with this meaning. For the fruit of the mulberry is at first white in the blossom, and being formed from thence grows red, and blackens as it gets ripe. The devil also having by transgression fallen from the white flower of the angelic nature and the bright beams of his power, grows terrible in the black odor of sin.

The mulberry may be also compared to the devil, for as by the leaves of the mulberry tree certain worms are fed, so the devil, by the imaginations which proceed from him, is feeding for us a never dying worm; but this mulberry tree faith is able to pluck out of our souls, and plunge it into the deep.

For, in fine, the agreement and harmony of the faith of both contribute to one end, salvation. We have in the apostle an unerring witness: “For I desire to see you, that I may impart unto you some spiritual gift, in order that ye may be strengthened; that is, that I may be comforted in you, by the mutual faith of you and me.” And further on again he adds, “The righteousness of God is revealed from faith to faith.” The apostle, then, manifestly announces a twofold faith, or rather one which admits of growth and perfection; for the common faith lies beneath as a foundation. To those, therefore, who desire to be healed, and are moved by faith, He added, “Thy faith hath saved thee.” But that which is excellently built upon is consummated in the believer, and is again perfected by the faith which results from instruction and the word, in order to the performance of the commandments. …

2. He professes in the first place to be replying to insinuations made at Rome against his orthodoxy, he being a man most fully approved in respect both of divine faith and of charity. He says that he would have wished to come himself, were it not that he had lately returned, after thirty years’ absence, to his parents, and that it would have seemed harsh and inhuman to leave them after having been so long in coming to them; and also if he had not become somewhat less robust through his long and toilsome journey, and too infirm to begin his labours again. As he had not been able to come himself, he had sent his apology as a kind of literary cudgel which the bishop might hold in his hand and drive away the dogs who were raging against him. …

xvii. 6 . The Apostles’ faith was not even like a grain of mustard seed.