1 Corinthians 9:20

And to the Jews I was as a Jew, so that I might give the good news to them; to those under the law I was the same, not as being myself under the law, but so that I might give the good news to those under the law.

Acts 16:3

Paul had a desire for him to go with him, and he gave him circumcision because of the Jews who were in those parts: for they all had knowledge that his father was a Greek.

Acts 21:20-26

And hearing it, they gave praise to God; and they said to him, You see, brother, what thousands there are among the Jews, who have the faith; and they all have a great respect for the law:

Acts 17:2-3

And Paul, as he generally did, went in to them, and on three Sabbath days had discussions with them from the holy Writings,

Acts 18:18

And Paul, after waiting some days, went away from the brothers and went by ship to Syria, Priscilla and Aquila being with him; and he had had his hair cut off in Cenchrea, for he had taken an oath.

Romans 3:19

Now, we have knowledge that what the law says is for those who are under the law, so that every mouth may be stopped, and all men may be judged by God:

Romans 6:14-15

For sin may not have rule over you: because you are not under law, but under grace.

Romans 11:14

If in any way those who are of my flesh may be moved to envy, so that some of them may get salvation by me.

Galatians 4:5

That he might make them free who were under the law, and that we might be given the place of sons.

Galatians 4:21

Say, you whose desire it is to be under the law, do you not give ear to the law?

Galatians 5:18

But if you are guided 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 had a desire for him to go with him, and he gave him circumcision because of the Jews who were in those parts: for they all had knowledge that his father was a Greek.
Acts 17:2
And Paul, as he generally did, went in to them, and on three Sabbath days had discussions with them from the holy Writings,
Acts 18:18
And Paul, after waiting some days, went away from the brothers and went by ship to Syria, Priscilla and Aquila being with him; and he had had his hair cut off in Cenchrea, for he had taken an oath.
Acts 21:20
And hearing it, they gave praise to God; and they said to him, You see, brother, what thousands there are among the Jews, who have the faith; and they all have a great respect for the law:

Are under

Romans 3:19
Now, we have knowledge that what the law says is for those who are under the law, so that every mouth may be stopped, and all men may be judged by God:
Romans 6:14
For sin may not have rule over you: because you are not under law, but under grace.
Galatians 4:5
That he might make them free who were under the law, and that we might be given the place of sons.
Galatians 5:18
But if you are guided by the Spirit, you are not under the law.

General references

Luke 11:37
Now, while he was talking, a Pharisee made a request that he would come to a meal with him; and he went in and took his seat at the meal.
Romans 15:2
Let every one of us give pleasure to his neighbour for his good, to make him strong.
1 Corinthians 10:33
Even as I give way to all men in all things, not looking for profit for myself, but for the good of others, that they may get salvation.
Galatians 2:3
But not even Titus who was with me, being a Greek, was made to undergo circumcision:

Basic English, produced by Mr C. K. Ogden of the Orthological Institute - public domain