1 Corinthians 9:20

And to 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;

Acts 16:3

Him would Paul have to go forth with him; and took and circumcised him, because of the Jews who were in those quarters: for they all knew that his father was a Greek.

Acts 21:20-26

And when they heard it, they glorified the Lord, and said to him, Thou seest, brother, how many thousands of Jews there are who believe; and they are all zealous of the law:

Acts 17:2-3

And Paul, as his manner was, went in to them, and on three sabbaths reasoned with them out of the scriptures,

Acts 18:18

And Paul after this tarried there yet a good while, and took his leave of the brethren, and sailed thence into Syria, and with him Priscilla and Aquila; having shorn his head in Cenchrea: for he had a vow.

Romans 3:19

Now we know that whatever things the law saith, it saith to them who are under the law: that every mouth may be stopped, and all the world may become guilty before God.

Romans 6:14-15

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

Romans 11:14

If by any means I may incite to emulation them who are my flesh, and may save some of them.

Galatians 4:5

To redeem them that were under the law, that we might receive the adoption of sons.

Galatians 4:21

Tell me, ye that desire to be under the law, do ye not hear the law?

Galatians 5:18

But if ye are led by the Spirit, ye 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
Him would Paul have to go forth with him; and took and circumcised him, because of the Jews who were in those quarters: for they all knew that his father was a Greek.
Acts 17:2
And Paul, as his manner was, went in to them, and on three sabbaths reasoned with them out of the scriptures,
Acts 18:18
And Paul after this tarried there yet a good while, and took his leave of the brethren, and sailed thence into Syria, and with him Priscilla and Aquila; having shorn his head in Cenchrea: for he had a vow.
Acts 21:20
And when they heard it, they glorified the Lord, and said to him, Thou seest, brother, how many thousands of Jews there are who believe; and they are all zealous of the law:

Are under

Romans 3:19
Now we know that whatever things the law saith, it saith to them who are under the law: that every mouth may be stopped, and all the world may become guilty before God.
Romans 6:14
For sin shall not have dominion over you: for ye are not under the law, but under grace.
Galatians 4:5
To redeem them that were under the law, that we might receive the adoption of sons.
Galatians 5:18
But if ye are led by the Spirit, ye are not under the law.

General references

Luke 11:37
And as he was speaking, a certain Pharisee besought him to dine with him: and he went in, and sat down to eat.
Romans 15:2
Let every one of us please his neighbor for his good to edification.
1 Corinthians 10:33
Even as I please all men in all things, not seeking my own profit, but the profit of many, that they may be saved.
Galatians 2:3
But neither Titus, who was with me, being a Greek, was compelled to be circumcised: