Christian liberty is one of those great biblical truths the Protestant Reformers recovered. The papacy had made all sorts of rules, regulations, doctrines, and so forth that were neither commanded nor taught by Scripture. The Reformers, thinking of texts like Matthew 15:9, Acts 5:29, Galatians 5:1 (and so on), said that to believe man-made doctrines or to obey man-made religious laws destroys the freedom of the conscience (see WCF 20.2).
The Reformers also talked about Christian liberty in terms of the gospel, that our consciences are be free from the terrors of the law because Christ obeyed in our place and paid for all our sins. Justification by faith alone is very closely related to Christian liberty!
John Calvin said the following:
“…Christian freedom is, in all its parts, a spiritual thing. Its whole force consists in quieting frightened consciences before God – that are 1) perhaps disturbed and troubled over forgiveness of sins, or 2) anxious whether unfinished works, corrupted by the faults of our flesh, are pleasing to God, or 3) tormented about the use of things indifferent (Institutes, III.XIX.8)”
Of course, Christian liberty has a few angles to it. It also means we should obey God and seek to be holy – Christ saved us to do good works! (Eph. 2:10). I also appreciate how Naselli and Crowley explained Christian liberty as they reflect on 1 Corinthians 9:19 and the surrounding context:
“Christian liberty isn’t, ‘Cool! I finally get to do the stuff I’ve always wanted to but my strict upbringing wouldn’t let me. Then you Facebook about it so that everyone knows you’re hip. That’s not Christian liberty; that’s immaturity. Christian liberty is the domain of the mature, not the immature. When the immature get ahold of it, they make a mess of it, like some of the Corinthians did.
Christian liberty is not about you and your freedom to do what you want to do. It’s about the freedom to discipline yourself to be flexible for the sake of the gospel and for the sake of weaker believers.”
In summary, Christian liberty 1) frees us from man-made laws and doctrines, 2) is based upon the gospel and justification by faith alone, and 3) isn’t about doing whatever you want to do, but in self-control being flexible for the sake of the gospel. Here’s Calvin again:
“Nothing is plainer than this rule: that we should use our freedom if it results in the edification of our neighbor, but if it does not help our neighbor, then we should forego it.”
The above quote by Naselli and Crowley is found on page 132 of Conscience: What It Is, How to Train It, and Loving Those Who Differ.