Luke 3:9

If the completion of all things had been then already begun, and the end of time close at hand, I should have no question but that the prophecy was given, because at that time it was to be fulfilled. But now that many ages have elapsed since the Spirit spoke this, I think it was prophesied to the people of Israel, because their cutting off was approaching. For to those that went out to him that they should be baptized, he gave this warning among others.

It is elegantly said, that beareth not fruit, and it is added, good. For God created man an animal fond of employment, and constant activity is natural to him, but idleness is unnatural. For idleness is hurtful to every member of the body, but much more to the soul. For the soul being by nature in constant motion does not admit of being slothful. But as idleness is an evil, so also is an unworthy activity. But having before spoken of repentance, he now declares that the axe lies near, not indeed actually cutting, but only striking terror.

By the axe then he declares the deadly wrath of God, which fell upon the Jews on account of the impieties they practised against Christ; he does not pronounce the axe to be yet fixed to the root, (ad radicem) but that it was laid, i. e. near the root. For though the branches were cut down, the tree itself was not yet entirely destroyed. For a remnant of Israel shall be saved.

(ubi sup.) Or we may take it in this way; The tree represents the whole human race in this world, but the axe is our redeemer, who by the handle and iron, as it were, is held indeed in the hand of man, but strikes by the power of God. Which axe indeed is now laid at the root of the tree; for although it waits patiently, yet it is plain what it is about to do. And we must observe that the said axe is to be laid not at the branches, but at the root. For when the children of the wicked are taken away, what is this but the cutting off of the branches of an unfruitful tree. But when the whole family together with the parent is removed, the unfruitful tree is cut off from the very root. But every hardened sinner finds the fire of hell the quicker prepared for him, as he disdains to bring forth the fruits of good works. Hence it follows, Every one then.

But although God can alter and change the most diverse natures, yet in my mind a mystery is of more avail than a miracle. For what else than stones were they who bowed down to stones, like indeed to them who made them. It is prophesied therefore that faith shall be poured into the stony hearts of the Gentiles, and through faith the oracles promise that Abraham shall have sons. But that you may know who are the men compared to stones, he has also compared men to trees, adding, For now the axe is laid to the root of the tree. This change of figure was made, that by means of comparison might be understood to have now commenced a more kindly growth of manhood. Let him then that is able bring forth fruit unto grace, him who ought, unto repentance. The Lord is at hand seeking for His fruit, who shall cherish the fruitful, but rebuke the barren.