For though I am free from all, I have made myself a servant to all, that I might win more of them. To the Jews I became as a Jew, in order to win Jews. To those under the law I became as one under the law (though not being myself under the law) that I might win those under the law. To those outside the law I became as one outside the law (not being outside the law of God but under the law of Christ) that I might win those outside the law. To the weak I became weak, that I might win the weak. I have become all things to all people, that by all means I might save some. I do it all for the sake of the gospel, that I may share with them in its blessings. (1 Cor 9:19-23).
Notice the section in bold. I never noticed this before, but Paul is making a distinction between the “law” of the Jews and the “law of God” or the “law of Christ.” Paul became someone both inside and outside the law of the Jews, but not outside the law of God. What, then, is the law of the Jews? In Romans 2 Paul talks about the Jews who consider themselves true Jews because they follow the law of physical circumcision. Paul explains that true circumcision is of the heart, “not by the written code.” In Galatians 3 Paul talks about how the purpose of Jewish law was to bring us to Christ in faith (Gal. 3:24). But the law is not a means to salvation in itself. Salvation is only by grace through faith in Christ. Our hope cannot be in Jewish law, because it is a dead end.

So what exactly is being “under the law of Christ?” Paul makes this very plain in Romans 6:

“Let not sin therefore reign in your mortal body, to make you obey its passions. Do not present your members to sin as instruments for unrighteousness, but present yourselves to God as those who have been brought from death to life, and your members to God as instruments for righteousness. For sin will have no dominion over you, since you are not under law but under grace.”

In retrospect, this is actually a great passage for heretics who proclaim an anti-nomian type theology, which attempts to give freedom to commit all sorts of sin. But this passage will not allow for that type of lifestyle. The contrast between grace and law has nothing to do with what we can “get away with,” but everything that we are and should be as sinless instruments of righteousness. To live in grace, to be free in Christ apart from Jewish law or any law is simply to obey and follow Christ. True living is to live freely from the passions and lusts of our flesh. It is the freedom to choose against our self-centered will, and instead live as the servant-minded creatures we were made to be. We were created to live outwardly — to give, to love, to bring, to help, doing all of these things not with a self-serving attitude or purpose, but rather with the purpose of loving Christ and being free in Him.