“All things are lawful,” but not all things are helpful (1 Corinthians 10:23).
As a Christian grows in Christ, he becomes less interested in what is lawful, and more interested in what is helpful. This is not because he does not believe in the law, or considers himself above it, but rather because he understands in ever-increasing measure that the law was meant to be helpful. Let me use Paul’s words concerning food offered to idols, from which the line quoted above was taken, to explain.
In the Old Testament, Israel was given certain dietary laws which allowed some meats and forbade others. The OT never gives a specific reason why it was OK to eat lamb but not pork, or trout but not crab, but it does suggest that Israel was given these laws to separate her from the surrounding nations, therefore guarding her from the temptation to follow the gods and customs of those nations. In other words, we are not told that eating certain meats was intrinsically evil, but we are told that not eating certain meats restricted the fellowship Israel might share with other nations. That is part of what it meant for Israel to be holy—different and distinct from the nations of the world.
In the New Testament, these dietary laws no longer apply to the people of God. But the spirit behind those laws does. A Christian—whether a Gentile Christian or a Jewish Christian—could eat whatever he pleased with thanks to God, for he knew that “the earth is the Lord’s, and the fullness thereof” (1 Cor. 10:26; cf. Ps 24:1). But that didn’t mean that he always ate anything he pleased. Paul gives an example of one who is presented with meat, having been told that it had been offered to idols. The Christian at that point does not eat that meat, not because there is anything intrinsically wrong with it, but because he does not want in any way to participate, or appear to participate, in idolatry. Just like Israel in the Old Testament, the Christian will have nothing to do with the gods of the nations, and he will take care to ensure others know it, lest he confuse them by implying that one can serve both Christ and idols. Eating that meat might be lawful, but it would certainly not be helpful. And therefore he does not do it.
As one grows in Christ, the question becomes less “am I allowed to do this?” but rather “will this encourage my walk with and witness to Christ?” The question is not whether I am allowed to buy a certain thing, but whether what I buy would serve the glory of God in some way. The question is not whether I am allowed to listen to certain music or watch certain movies, but whether so doing will move me closer to Jesus and his intentions for me. There are many ways one can spend his time without breaking any law—am I spending mine in ways that honor God and bless my neighbor?
In the end, the controlling questions concerning matters of law is this—does this thing (what ever this thing is) encourage me in my love of God and my neighbor? Does it draw me closer to God? Does it serve my neighbor well? These questions are of a different order than “am I allowed to do this?” In the end, one set of questions is all about me. The other set of questions is all about God, and my neighbor. One set of questions is legalistic, serving the letter of the law, and is primarily concerned with what I can or cannot do. The other set of questions serves the spirit of the law, and is not primarily concerned with me, but rather with loving God and neighbor.
Perhaps this is what was meant when the Lord promised in the Old Testament that one day he would write the law upon the hearts of his people (Jeremiah 31:31-34).