12 Repentance for sins changes men, it is true, for the better; but it does not appear as if even it would profit ought, if it should be barren of works of mercy. This the Truth testifies by the mouth of John, who said to them that came to him, “O generation of vipers, who has warned you to flee from the wrath to come? Bring forth therefore fruits worthy of repentance; And say not we have Abraham to our father; for I say unto you, that God is able of these stones to raise up children unto Abraham.
For now is the axe laid unto the root of the trees. Every tree therefore that brings not forth good fruit shall be cut down, and cast into the fire.” Touching this fruit he said above, “Bring forth fruits worthy of repentance.” Whoso then brings not forth these fruits, has no cause to think that he shall attain pardon for his sins by a barren repentance. Now what these fruits are, he shows afterwards himself. For after these his words the multitude asked him, saying, “What shall we do then?”
That is, what are these fruits, which you exhort us with such alarming force to bring forth? “But he answering said unto them, he that has two coats, let him give to him that has none; and he that has meat, let him do likewise.” My brethren, what is more plain, what more certain, or express than this? What other meaning then can that have which he said above, “Every tree that brings not forth good fruit, shall be cut down, and cast into the fire;” but that same which they on the left shall hear, “Go ye into everlasting fire, for I was hungry, and you gave Me no meat.”
So then it is but a small matter to depart from sins, if you shall neglect to cure what is past, as it is written, “Son, you have sinned, do so no more.” And that he might not think to be secure by this only, he says, “And for your former sins pray that they may be forgiven you.” But what will it profit you to pray for forgiveness, if you shall not make yourself meet to be heard, by not bringing forth fruits meet for repentance, that you should be cut down as a barren tree, and be cast into the fire? If then ye will be heard when you pray for pardon of your sins, “Forgive, and it shall be forgiven you; Give, and it shall be given you.”
Source: Sermons on Selected Lessons of the New Testament (New Advent)