It is implied that Christ has set believers free from the old covenant. Here freedom from the old covenant is a metaphor for not being obligated to obey it. AT: "You were called to freedom from the old covenant" or "Christ has chosen you to not be obligated to the old covenant" (See: [[rc://en/ta/man/translate/figs-metaphor]])
The relationship between the opportunity and the sinful nature can be stated more clearly. AT: "an opportunity for you to behave according to your sinful nature" (See: [[rc://en/ta/man/translate/figs-explicit]])
Possible meanings are 1) "you can state the whole law in just one commandment, which is this" or 2) "by obeying one commandment, you obey all the commandments, and that one commandment is this."