Here's more context Jesus was condemning those who keep their own rules over obeying the commandments of God quoting directly from the Ten Commandments
Mat 15: 3 He answered and said to them, “Why do you also transgress the commandment of God because of your tradition? 4 For God commanded, saying, ‘Honor your father and your mother’; and, ‘He who curses father or mother, let him be put to death.’ 5 But you say, ‘Whoever says to his father or mother, “Whatever profit you might have received from me is a gift to God”— 6 then he need not honor his father [a]or mother.’ Thus you have made the [b]commandment of God of no effect by your tradition. 7 Hypocrites! Well did Isaiah prophesy about you, saying:
8 ‘These people [c]draw near to Me with their mouth,
And honor Me with their lips,
But their heart is far from Me.
9 And in vain they worship Me,
Teaching as doctrines the commandments of men.’ ”
Which goes with
And then I will declare to them, ‘I never knew you; depart from Me, you who practice lawlessness!’
1 John 2:3 Now by this we know that we know Him, if we keep His commandments. 4 He who says, “I know Him,” and does not keep His commandments, is a liar, and the truth is not in him.
Good example of how they transgressed scripture especially verse 4, where they were instructed to kill the person. Yet they took profits instead making it have no effect.
Yeah in the OT, it was a serious offense and death was to be carried out. They practiced lawlessness by not killing, the old testament didn't play around.
Matt 15:4 For God commanded, saying, ‘Honor your father and your mother’; and, ‘He who curses father or mother, let him be put to death.’