John Chrysostom — as excerpted in the Catena Aurea on Matthew 15:1-6

“He desired to shew the great honour that ought to be paid to parents, and therefore attached both a reward and a penalty. But in this occasion the Lord passes over the reward promised to such as did honour their parents, namely, that they should live long upon the earth, and brings forward the terrible part only, namely, the punishment, that He might strike these dumb and attract others; And he that curseth father and mother, let him die the death; thus He shews that they deserved even death. For if ho who dishonours his parent even in word is worthy of death, much more ye who dishonour him in deed; and ye not only dishonour your parents, but teach others to do so likewise. Ye then who do not deserve even to live, how accuse ye my disciples? But how they transgress the commandment of God is clear when He adds, But ye say, Whoso shall say to his father or his mother, If in a gift, whatsoever thou mightest be profited by me.”