1 Corinthians 9:20

And to the Jews I became as a Jew, so that I might gain Jews, to those under law, as under law, so that I might gain those under law,

Acts 16:3

Paul wanted this man to go forth with him. And having taken him, he circumcised him because of the Jews who were in those regions, for they had all seen that his father was a Greek.

Acts 21:20-26

And when the men heard, they glorified God, having said to him, Thou see, brother, how many thousands there are of the Jews who have believed, and they are all zealots of the law.

Acts 17:2-3

And according to Paul's custom, he went in to them, and for three Sabbaths he discoursed with them from the Scriptures,

Acts 18:18

But Paul, who still remained considerable days with the brothers, having separated, sailed away to Syria (and with him Priscilla and Aquila), having shaved his head in Cenchrea, for he had a vow.

Romans 3:19

Now we know that as many things as the law says, it says to those in the law, so that every mouth may be stopped, and all the world may become accountable to God.

Romans 6:14-15

for sin will not have dominion over you. For ye are not under law, but under grace.

Romans 11:14

if somehow I may provoke my flesh to jealousy and may save some of them.

Galatians 4:5

so that he might redeem those under law, so that we might receive the sonship.

Galatians 4:21

Tell me those desiring to be under law, do ye not hear the law?

Galatians 5:18

But if ye are led by Spirit ye are not under law.

Treasury of Scripture Knowledge

Summary

And unto the Jews I became as a Jew, that I might gain the Jews; to them that are under the law, as under the law, that I might gain them that are under the law;

Bible References

Unto

Acts 16:3
Paul wanted this man to go forth with him. And having taken him, he circumcised him because of the Jews who were in those regions, for they had all seen that his father was a Greek.
Acts 17:2
And according to Paul's custom, he went in to them, and for three Sabbaths he discoursed with them from the Scriptures,
Acts 18:18
But Paul, who still remained considerable days with the brothers, having separated, sailed away to Syria (and with him Priscilla and Aquila), having shaved his head in Cenchrea, for he had a vow.
Acts 21:20
And when the men heard, they glorified God, having said to him, Thou see, brother, how many thousands there are of the Jews who have believed, and they are all zealots of the law.

Are under

Romans 3:19
Now we know that as many things as the law says, it says to those in the law, so that every mouth may be stopped, and all the world may become accountable to God.
Romans 6:14
for sin will not have dominion over you. For ye are not under law, but under grace.
Galatians 4:5
so that he might redeem those under law, so that we might receive the sonship.
Galatians 5:18
But if ye are led by Spirit ye are not under law.

General references

Luke 11:37
Now as he spoke a certain Pharisee asks him that he might dine with him. And having entered in, he sat down.
Romans 15:2
Let each of us please his neighbor for what is good toward edification.
1 Corinthians 10:33
just as I also strive to please in all things for all men, not seeking my own advantage, but that of the many, so that they may be saved.
Galatians 2:3
But not even Titus with me, being a Greek, was compelled to be circumcised.