The Traditions of the Elders in Collision with Divine Law
But let us return to the subject before us, in which the Saviour abridged and expounded two commandments from the law, the one from the decalogue from Exodus, and the other from Leviticus, or the other from some one of the books of the Pentateuch. Then since we have explained in what way they made void the word of God which said, “Honour your father and your mother,” by saying, “You shall not honour your father or your mother,” whosoever shall say to his father or mother, “It is a gift that wherewith you might have been profited by me,” some one may inquire whether the words, “He that speaks evil of father or mother, let him die the death,” are not extraneous.
For, granted that he does not honour his father and mother, who consecrates to what is called Corban that which would have been given in honour of father and mother, in what way, therefore, does the tradition of the Pharisees make void the word which said, “He that speaks evil of father or mother, let him die the death?” But, perhaps, when any one said to his father or his mother, “It is a gift, that wherewith you might have been profited by me,” he, as it were, casts abuse on his father or mother as if he were calling his parents sacrilegious, in taking that which was consecrated to Corban from him who had consecrated it to Corban.
The Jews then punish their sons according to the law, as speaking evil of father or mother, when they say to their father or mother, “It is a gift, that wherewith you might have been profited by me,” but you by one of your traditions make void two commandments of God. And then you are not ashamed to accuse My disciples who transgress no commandment; for they walk “in all His commandments and ordinances blamelessly,” but transgress a tradition of the elders, so as not to transgress a commandment of God.
And if you had held this aim before you, you would have kept the commandment about the honour due to father and mother, and that which said, “He that speaks evil of father and mother, let him die the death;” but the tradition of the elders which is opposed to these commandments you would not have kept.
Source: Commentary on the Gospel of Matthew (New Advent)