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.)

To the Jews he would observe the Mosaic customs as long as it did not affect his duty to Christ.  There was no compromise of principles or the law though Paul was a Jew among Jews. He did not act as a person obligated to the law with the Jews, nor as a lawless person to the Gentiles, but always made it evident he was serving them under the law of Christ.

An example of reaching the gentiles 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.  He was brought to Mars Hill where the finest philosophers and seekers congregated. He used what the Athenians did not know, an altar to an unknown god to make known to them what he knew (Acts 17). V.23 “the One whom you worship without knowing, Him I proclaim to you.” Paul was not complimenting their religious worship as they were idolaters. In v.30 Paul did not mock them but gave it to them straight "Truly, these times of ignorance God overlooked, but now commands all men everywhere to repent.” These religious men of prestige were offended as he told them they would be judged by a man who came back to life (Acts 17:31-33).

Acts 17:16 Paul saw the city was given over to idols but did not confront them because he was appealing to the men who were learners of religions and philosophies. But to others he did

1 Cor. 12:2 You know that you were Gentiles, carried away to these dumb idols

1Thess. 1:9 they “turned to God from idols to serve the living and true God”

Paul certainly made a distinction (as did Jesus) of those who knew what God required and those in ignorance. Paul even pitted the Gentiles against the Jews to humble them from pride. Rom 2:14-16 for when Gentiles, who do not have the law, by nature do the things in the law, these, although not having the law, are a law to themselves, who show the work of the law written in their hearts, their conscience also bearing witness, and between themselves their thoughts accusing or else excusing them) in the day when God will judge the secrets of men by Jesus Christ, according to my gospel.” (giving the same summation as he did in Acts 17)

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 for one to reach a drug addict they must become one, one cannot reach a drunk unless they drink alcohol etc.

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 to win them. 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 and receive.

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 overeaters, he would not become a drug user to reach the addict, he would not become a drinker of alcohol to reach a drunk.

It goes back to the overarching introduction: 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.” Paul put himself in a humble state with the other person’s welfare in mind.

Paul simply meant that he would use their own beliefs and ways to show them the actual 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 to illustrate what they needed to know about Jesus.