4 Mark then how by what follows also he increases their alarm, and adds intensity to their agonizing fear.
For having said that “God is able of these stones to raise up children unto Abraham,” he added, “And now also the axe is laid unto the root of the trees,” by all means making his speech alarming. For as he from his way of life had much freedom of speech, so they needed his severe rebuke, having been left barren now for a long time. For “why do I say” (such are his words) that you are on the point of falling away from your relationship to the patriarch and of seeing others, even those that are of stones, brought in to your pre-eminence? Nay, not to this point only will your penalty reach, but your punishment will proceed further. “For now,” says he, “the axe is laid unto the root of the trees.” There is nothing more terrible than this turn of his discourse. For it is no longer “a flying sickle,” nor “the taking down of a hedge,” nor “the treading under foot of the vineyard;” but an axe exceeding sharp, and what is worse, it is even at the doors. For inasmuch as they continually disbelieved the prophets, and used to say, “Where is the day of the Lord:” and “let the counsel of the Holy One of Israel come, that we may know it,” by reason that it was many years before what they said came to pass; to lead them off from this encouragement also, he sets the terrors close to them. And this he declared by saying “now,” and by his putting it to “the root.” “For the space between is nothing now,” says he, “but it is laid to the very root.” And he said not, “to the branches,” nor “to the fruits,” but “to the root.” Signifying, that if they were negligent, they would have incurable horrors to endure, and not have so much as a hope of remedy. It being no servant who is now come, as those before Him were, but the very Lord of all, bringing on them His fierce and most effectual vengeance.
Yet, although he has terrified them again, he suffers them not to fall into despair; but as before he said not “He has raised up,” but “He is able to raise up children to Abraham” (at once both alarming and comforting them); even so here also he did not say that “it has touched the root,” but “it is laid to the root, and is now hard by it, and shows signs of no delay.” However, even though He has brought it so near, He makes its cutting depend upon you. For if you change and become better men, this axe will depart without doing anything; but if you continue in the same ways, He will tear up the tree by the roots. And therefore, observe, it is neither removed from the root, nor applied as it is does it cut at all: the one, that you may not grow supine, the other to let you know that it is possible even in a short time to be changed and saved. Wherefore he does also from all topics heighten their fear, thoroughly awakening and pressing them on to repentance. Thus first their falling away from their forefathers; next, others being introduced instead; lastly, those terrors being at their doors, the certainty of suffering incurable evils (both which he declared by the root and the axe), was sufficient to rouse thoroughly those even that were very supine, and to make them full of anxiety. I may add, that Paul too was setting forth the same, when he said, “A short word will the Lord make upon the whole world.”
But be not afraid; or rather, be afraid, but despair not. For you have yet a hope of change; the sentence is not quite absolute, neither did the axe come to cut (else what hindered it from cutting, close as it was to the root?); but on purpose by this fear to make you a better man, and to prepare you to bring forth fruit. For this cause he added, “Therefore every tree, which brings not forth good fruit, is hewn down, and cast into the fire.” Now by the word “every,” he rejects again the privilege which they had from their noble descent; “Why, if you be Abraham's own descendant,” says he, “if you have thousands of patriarchs to enumerate, you will but undergo a double punishment, abiding unfruitful.”
By these words he alarmed even publicans, the soldiers' mind was startled by him, not casting them into despair, yet ridding them of all security. For along with the terror, there is also much encouragement in what he says; since by the expression, “which brings not forth good fruit,” he signified that what bears fruit is delivered from all vengeance.
Source: Homilies on the Gospel of St. Matthew (New Advent)