1 Corinthians 9:19: “For though I am free from all men, I have made myself a servant to all, that I might win the more; 20 and to the Jews I became as a Jew, that I might win Jews; to those who are under the law, as under the law, that I might win those who are under the law; 21 to those who are without law, as without law (not being without law toward God, but under law toward Christ), that I might win those who are without law; 22 to the weak I became as weak, that I might win the weak. I have become all things to all men, that I might by all means save some. 23 Now this I do for the gospel's sake, that I may be partaker of it with you.”

What did Paul mean that he became all things to all men for evangelism? This is his summation after he describes his goal and those people whom he wanted to reach.

He adapted his teaching to their thought in their culture to reach them. He divides the world into the religious with the law, (Jews) and the Gentiles, without the law.

1 Corinthians 9:20 Not being myself under the law mee (NT:3319) oon (NT:5541) autos (NT:839) hupo (NT:5201) nomon (NT:3506). He was emancipated from the law as a means of salvation, yet he knew how to speak to them because of his former beliefs and life with them (Galatians 4:21). He knew how to put the gospel to them without compromise and without offence (from Robertson's Word Pictures in the New Testament.)

An example of this is recorded in Acts 17. He showed the philosophers they were wrong from logic, their own history and the Bible and explained to them what is right.

In 1 Corinthians 9:22 Paul said by inspiration of the Holy Spirit: “To the weak became I as weak, that I might gain the weak: I am made all things to all men, that I might by all means save some.”

If this is isolated from the rest of Scripture one can assume that Paul was willing to do anything to reach the lost, including adopting their lifestyle and compromise his ethics, moral and beliefs. This is a doctrine that is popularized among the seeker friendly evangelism crowd today. If we use this logic then one cannot reach a drug addict unless they become one, one cannot reach a drunk unless they drink alcohol.

When we compare Scripture with Scripture, we find that Paul did not mean this. Paul taught that believers are to “abstain from any appearance of evil” (1 Thess. 5:22). Paul would not have done anything contrary to Christ and his ways in his own life and ministry. Remember he rebuked Peter for his compromise of the gospel to the Jewish brethren. Galatians 2:12-13 speaking of the Judaizers “for before certain men came from James, he would eat with the Gentiles; but when they came, he withdrew and separated himself, fearing those who were of the circumcision. “Saying to Peter Galatians 2:14 “If you, being a Jew, live in the manner of Gentiles and not as the Jews, why do you compel Gentiles to live as Jews?

So Paul did not mean that we act one way with one group of people and another way with another group.

In 1 Cor. 9:21, for example, he says, “To them that are without law, as without law, (BEING NOT WITHOUT LAW TO GOD, BUT UNDER THE LAW TO CHRIST,) that I might gain them that are without law.”

To them that are without law. We have good examples how Paul acted among the pagans, those outside the Mosaic law (Romans 2:14), not lawless (Luke 22:37; Acts 2:23; 1 Timothy 1:9). Paul simplified the message knowing his audience so they could understand.

Paul explains that he is always under the law to Christ and he is never free to do things that would be contrary to the new covenant. And in Galatians 5:13 he says, “For, brethren, ye have been called unto liberty; ONLY USE NOT LIBERTY FOR AN OCCASION TO THE FLESH, but by love serve one another.”

Paul’s liberty in his evangelism was not a freedom to serve the flesh in any way. Paul was always strict in regard to sin and he did not allow anything in his life that would bring the result of sin by spiritual carelessness. He would not become a glutton to reach other overeaters, he would not become a drug user to reach the addict, he would not become a drinker of alcohol to reach a drunk.
And in 1 Cor. 9:27 Paul says, “But I discipline my body and BRING IT INTO SUBJECTION: lest that by any means, when I have preached to others, I myself should become disqualified (a castaway)”

Paul simply meant that he would use their own beliefs and ways to show them the truth. So to a religious Jew he would use the law to speak to them, to a gentile he would use his conscience and culture .