Christian liberty and liberty of the conscience are rich concepts (see the Westminster Confession of Faith 20:1 and 2). In Christ we have been set free from bondage to Satan, sin, and death. We are no longer bound by the ceremonial law, but have direct access to God in Christ Jesus by his Spirit. The conscience is bound, not by regulations of men, but by the Word of God. We may not forbid what God allows nor require what God does not command.
We can also use the term “Christian liberty” to refer to how we use things which are not wrong in themselves. John Murray in “The Weak and the Strong” (originally published in the Westminster Theological Journal, Vol. XII, 2, 1950, reprinted in Vol. 4 of his Collected Writings, pp. 142-157, and available online at: http://www.reformedliterature.com/murray-the-weak-and-the-strong.php), discusses the classic passages, Romans 14 and 1 Corinthians 8. He identifies the issues involved in these Scriptures and carefully outlines the respective responsibilities of both the weaker and the stronger brother. A close reading of his article will benefit discussions of the subject of Christian liberty.
Murray reminds us that the issue is not things, but people:
It might appear that the question of the Christian’s use of things not wrong in themselves is a very simple one. To assert and maintain the intrinsic rightness or goodness of things in themselves might seem to be all that is necessary. But this is not the only thing to be considered. The question is complicated by the fact that when we are thinking of the actual use of things not wrong in themselves we are thinking of use by persons. . . . The problem becomes crystallized quite specifically in the consideration that Scripture itself takes into account the distinction between the weak and the strong, between those who are weak in faith and those who are strong in faith, between those whose consciences are weak and those whose consciences are strong. In a word, it is the problem of the weak and the strong.
In both Romans 14 and 1 Corinthians 8 Paul is dealing with weaker brothers who abstained from certain things on religious grounds.