Jamieson, Fausset and Brown on 1 Peter 2:16

16. As free--as "the Lord's freemen," connected with 1Pe 2:15, doing well as being free. "Well-doing" (1Pe 2:15) is the natural fruit of being freemen of Christ, made free by "the truth" from the bondage of sin. Duty is enforced on us to guard against licentiousness, but the way in which it is to be fulfilled, is by love and the holy instincts of Christian liberty. We are given principles, not details.

not using--Greek, "not as having your liberty for a veil (cloak) of badness, but as the servants of God," and therefore bound to submit to every ordinance of man (1Pe 2:13) which is of God's appointment.