Albert Barnes Commentary Matthew 15:4

"For God said, Honor thy father and thy mother: and, He that speaketh evil of father or mother, let him die the death." — Matthew 15:4 (ASV)

For God commanded, etc. That is, in the fifth commandment, Exodus 20:12; Exodus 21:17. To honour is to obey, to reverence, to speak kindly to, to speak and think well of. To curse is to disobey, to treat with irreverence, to swear at, to speak ill of, to think evil of in the heart, to meditate or do any evil to a parent. All this is included in the original word.

Let him die the death. This is a Hebrew phrase, the same as saying, let him surely die. The Jewish law punishes this crime with death. This duty of honouring and obeying a parent was what Christ said they had violated by their traditions. He proceeds to state the way in which it was done.

See Barnes on Matthew 15:1.