They were physically circumcised, and under the Law of Moses, as Acts 21:20.
They are not under the gospel of the uncircumcision (Galatians 2:7-9, Galatians 5:2)
Rightly divide:
Romans 2:28-29 ASV
28 For he is not a Jew who is one outwardly; neither is that circumcision which is outward in the flesh:
29
but he is a Jew who is one inwardly;
and circumcision is that of the heart, in the spirit not in the letter; whose praise is not of men, but of God.
There is no choice in the matter: those are emphatic statements which one either believes or does not believe.
Philippians 3:1-6 ASV
1 Finally, my brethren, rejoice in the Lord. To write the same things to you, to me indeed is not irksome, but for you it is safe.
2 Beware of the dogs, beware of the evil workers, beware of the concision:
3
for we are the circumcision,
who worship by the Spirit of God,
and glory in Christ Jesus,
and have no confidence in the flesh:
4 though I myself might have confidence even in the flesh: if any other man thinketh to have confidence in the flesh, I yet more:
5 circumcised the eighth day, of the stock of Israel, of the tribe of Benjamin, a Hebrew of Hebrews; as touching the law, a Pharisee;
6 as touching zeal, persecuting the church; as touching the righteousness which is in the law, found blameless.
1 Finally, my brethren, rejoice in the Lord. To write the same things to you, to me indeed is not irksome, but for you it is safe.
2 Beware of the dogs, beware of the evil workers, beware of the concision:
3 for we are the circumcision, who worship by the Spirit of God, and glory in Christ Jesus, and have no confidence in the flesh:
4 though I myself might have confidence even in the flesh: if any other man thinketh to have confidence in the flesh, I yet more:
5 circumcised the eighth day, of the stock of Israel, of the tribe of Benjamin, a Hebrew of Hebrews; as touching the law, a Pharisee;
6 as touching zeal, persecuting the church; as touching the righteousness which is in the law, found blameless.
This is another emphatic statement: "
for we are the circumcision".
And the following is yet another emphatic statement:
Romans 15:8-11 ASV
8 For I say
that Christ hath been made a minister of the circumcision for the truth of God,
that he might confirm the promises given unto the fathers,
9
and that the Gentiles might glorify God for his mercy; as it is written, Therefore will I give praise unto thee among the Gentiles, And sing unto thy name.
10 And again he saith,
Rejoice,
ye Gentiles,
with his people.
11 And again, Praise the Lord,
all ye Gentiles; And let all the peoples praise him.
Meshiah is the new Minister of the Circumcision, and therefore, because of these teachings herein above, Acts 15 is merely the entry-level position for the Gentile who desires to join Yisrael, as even was the case with Cornelius.
Cornelius had a Malak appear to him in the hour of prayer, the ninth hour which is one of the three prayer times: he was a righteous Gentile who set his heart with all his family to join the nation and people of Yisrael. After his appointed time he was no more a Gentile, circumcised the eighth day according to the Spirit, and according to the supernal Torah and the Prophets.