Paul speaks of "sin" here as if it were a king who rules over people. Alternate translation: "Do not let sinful desires control what you do" or "Do not allow yourselves to do the sinful things you want to do" (See: [[rc://en/ta/man/translate/figs-personification]])
To be "under law" means to be subject to its limitations and weaknesses. You can make the full meaning explicit in your translation. Alternate translation: "For you are no longer bound to the law of Moses, which could not give you the power to stop sinning" (See: [[rc://en/ta/man/translate/figs-explicit]])
To be "under grace" means that God's free gift provides the power to keep from sinning. You can make the full meaning explicit in your translation. Alternate translation: "but you are bound to God's grace, which does give you the power to stop sinning" (See: [[rc://en/ta/man/translate/figs-explicit]])