RobH_en_tn/num/15/31.md

has broken my commandment

Not obeying a commandment is spoken of as breaking it. Alternate translation: "has disobeyed my commandment" or "has not obeyed what I commanded" (See: rc://en/ta/man/translate/figs-metonymy)

His sin will be on him

Here "sin" represents either 1) punishment for that sin or 2) guilt of that sin. Sin being on him is a metaphor for either 1) being punished or 2) being guilty. Alternate translation: 1) "I will punish him because of his sin" or 2) "I will consider him guilty" (See: rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-metaphor)