Keepeth his own soul. Obedience to God's commandments preserves a man's natural and spiritual life (comp. Proverbs 13:13; Proverbs 16:17). So we read in Ecclesiastes 8:5, "Whoso keepeth the commandment (mitsvah, as here) shall feel no evil thing."
He that despiseth his ways shall die. He that cares nothing what he does, whether his life pleases God or not, shall perish. ἀπολεῖται, Septuagint; mortificabitur, Vulgate. The result is understood differently.
The Khetib reads, יוּמַת (iumath), "shall be punished with death" according to the penalties enacted in the Mosaic Law. The Keri reads, יָמוּת (iamuth), "shall die," as in Proverbs 15:10; and this seems more in agreement with what we find elsewhere in the book, as in Proverbs 10:21; Proverbs 23:13.
This insensate carelessness leads to ruin, whether its punishment be undertaken by outraged law. or whether it be left to the Divine retribution.