Why doesn't Paul use his freedom from the law as a license to sin?
Paul does not use his freedom from the law as a license to sin because the Holy Spirit controls every facet of his life. The Spirit never leads a believer into adultery or idolatry, so Paul refuses to be brought under the power of things the law forbids, even though all things are lawful for him.
Les explains that Paul, writing as a Jew, contrasts serving in newness of spirit with the oldness of the letter. Believers are no longer under the demands of the Ten Commandments of Moses but are under the control of the Holy Spirit. The Holy Spirit will never lead a believer to do something contrary to the law—never into adultery, never into idolatry. Without the burden of the law and the fear of breaking it, there is now grace, and the Holy Spirit leads, guides, and directs so that the law is kept under a whole different set of circumstances. Paul says all things are lawful for him because he is not under the law, but he will not be brought under the power of the things the law forbids. He is free from that burden, yet he will not take advantage of it or make license of it, because the Holy Spirit controls every facet of his life, and so it should be with us.
All things are lawful unto me, but all things are not expedient: all things are lawful for me, but I will not be brought under the power of any.