What is the meaning of Matthew 5:21?

Matthew 5:21 KJV
Ye have heard that it was said by them of old time, Thou shalt not kill; and whosoever shall kill shall be in danger of the judgment:

Matthew 5:21 NKJV
“You have heard that it was said to those of old, ‘You shall not murder, and whoever murders will be in danger of the judgment.’

Matthew 5:21 MKJV
You have heard that it was said to the ancients, “You shall not kill” –and, “Whoever shall kill shall be liable to the judgment.”

Matthew 5:21 KJV 2000
You have heard that it was said by them of old time, You shall not kill; and whosoever shall kill shall be in danger of the judgment:

Interlinear KJV

Ye have heard /akouo/ that /hoti/ it was said /rheo/ by them of old time, /archaios/ Thou shalt /phoneuo/ not /ou/ kill; /phoneuo/ and /de/ whosoever /hos/ /an/ shall kill /phoneuo/ shall be /esomai/ in danger /enochos/ of the judgment: /krisis/ {by: or, to}

Albert Barnes’ Commentary

Verse 21.  Ye have heard. Or, this is the common interpretation among the Jews. Jesus proceeds here to comment on some prevailing opinions among the Jews; to show that the righteousness of the scribes and Pharisees was defective; and that men needed a better righteousness, or they could not be saved. He shows what he meant by that better righteousness, by showing that the common opinions of the scribes were erroneous.  

By them of old time. This might be translated, to the ancients, referring to Moses and the prophets. But it is more probable that he here refers to the interpreters of the law and the prophets. Jesus did not set himself against the law of Moses, but against the false and pernicious interpretations of the law prevalent in his time.  

Thou shalt not kill. See Ex 20:13. This literally denotes taking the life of another, with malice, or with intention to murder him. The Jews understood it as meaning no more. The comment of our Saviour shows that it was spiritual, and was designed to extend to the thoughts and feelings, as well as the external act.  

Shall be in danger of. Shall be held guilty, and be punished by. The law of Moses declared that the murderer should be put to death, Le 24:21; Nu 35:16. It did not say, however, by whom this should be done, and it was left to the Jews to organize courts to have cognizance of such crimes, De 16:18.  

The judgment. This was the tribunal that had cognizance of cases of murder, etc. It was a court that sat in each city or town, and consisted commonly of seven members. It was the lowest court among the Jews, and from it an appeal might be taken to the Sanhedrim.  

{1} “by them” or, “to them”

{r} “Thou shalt not kill” Ex 20:13; De 5:17