1 Corinthians 9:20,21 - To the Jews I became like a Jew

9:20

So Paul lived like a Jew when amongst the Jews. He lived as one under the Law, so that he could win those under the Law. Paul was not looking at the Law as a means of salvation, but as the Law pointed towards Christ, he did not see the Law, given its proper place, as an obstacle. So he did not put any unnecessary obstacles in the way of Jews. The gospel itself is  a big enough obstacle, requiring man to humble himself.

9:21

Likewise, to the Gentiles he lived as one nut under the Law, so as not to put unnecessary obstacles in their way. For he did not want them thinking that in order to be saved they needed to be circumcised, or to follow certain food laws. They too needed to humble themselves, to repent and admit their need of Christ. Paul puts in a caveat, “I am not free from God’s law but am under Christ’s law”. He did not want people thinking they could live  licentiously as many of the Corinthians did.