1 Corinthians 9:20

To the Jews I became as a Jew, that I might gain Jews; to those who are under the law, as under the law, that I might gain those who are under the law;

Acts 16:3

Paul wanted to have him go out with him, and he took and circumcised him because of the Jews who were in those parts; for they all knew that his father was a Greek.

Acts 21:20-26

They, when they heard it, glorified God. They said to him, "You see, brother, how many thousands there are among the Jews of those who have believed, and they are all zealous for the law.

Acts 17:2-3

Paul, as was his custom, went in to them, and for three Sabbath days reasoned with them from the Scriptures,

Acts 18:18

Paul, having stayed after this many more days, took his leave of the brothers, and sailed from there for Syria, together with Priscilla and Aquila. He shaved his head in Cenchreae, for he had a vow.

Romans 3:19

Now we know that whatever things the law says, it speaks to those who are under the law, that every mouth may be closed, and all the world may be brought under the judgment of God.

Romans 6:14-15

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

Romans 11:14

if by any means I may provoke to jealousy those who are my flesh, and may save some of them.

Galatians 4:5

that he might redeem those who were under the law, that we might receive the adoption of children.

Galatians 4:21

Tell me, you that desire to be under the law, don't you listen to the law?

Galatians 5:18

But if you are led by the Spirit, you are not under the 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 to have him go out with him, and he took and circumcised him because of the Jews who were in those parts; for they all knew that his father was a Greek.
Acts 17:2
Paul, as was his custom, went in to them, and for three Sabbath days reasoned with them from the Scriptures,
Acts 18:18
Paul, having stayed after this many more days, took his leave of the brothers, and sailed from there for Syria, together with Priscilla and Aquila. He shaved his head in Cenchreae, for he had a vow.
Acts 21:20
They, when they heard it, glorified God. They said to him, "You see, brother, how many thousands there are among the Jews of those who have believed, and they are all zealous for the law.

Are under

Romans 3:19
Now we know that whatever things the law says, it speaks to those who are under the law, that every mouth may be closed, and all the world may be brought under the judgment of God.
Romans 6:14
For sin will not have dominion over you. For you are not under law, but under grace.
Galatians 4:5
that he might redeem those who were under the law, that we might receive the adoption of children.
Galatians 5:18
But if you are led by the Spirit, you are not under the law.

General references

Luke 11:37
Now as he spoke, a certain Pharisee asked him to dine with him. He went in, and sat at the table.
Romans 15:2
Let each one of us please his neighbor for that which is good, to be building him up.
1 Corinthians 10:33
even as I also please all men in all things, not seeking my own profit, but the profit of the many, that they may be saved.
Galatians 2:3
But not even Titus, who was with me, being a Greek, was compelled to be circumcised.