Ye were called for freedom (επ' ελευθερια εκληθητε). The same point as in Galatians 5:1 made plainer by the use of επ' (on the basis of, for the purpose of). See 1. Thessalonians 4:7 for this use of επ.

Only use not (μονον μη). No word for "use" in the Greek. Probably supply τρεπετε or στρεφετε, "turn not your liberty into an occasion for the flesh" (εις αφορμην τη σαρκ), as a spring board for license. On αφορμη, see on 2. Corinthians 5:12. Liberty so easily turns to license.