"It is so that we can be free that Christ has set us free." It is implied that Christ sets believers free from the law. Here freedom from the law is a metaphor for not being obligated to obey the law. (See: [[rc://en/ta/man/translate/figs-explicit]] and [[rc://en/ta/man/translate/figs-metaphor]])
Standing firm here represents being determined not to change. How they are not to change can be stated clearly. AT: "Do not give in to the arguments of people who teach something else" or "Be determined to stay free" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-explicit]])
Here being under control of a yoke of slavery represents being obligated to obey the law. AT: "do not live like one who is under the control of a yoke of slavery to the law" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-explicit]])