In Philippians 3, Paul is contrasting between those of the circumcision (sons of Jacob) at Philippi who not only were not Believers, and were out to do evil against those sons of Jacob like Paul, who were (Believers).
Philippians 3:1 Finally, my brethren, rejoice in the Lord. To write the same things to you, to me indeed is not grievous, but for you it is safe. 3:2 Beware of dogs, beware of evil workers, beware of the concision. 3:3 For we are the circumcision, which worship God in the spirit, and rejoice in Christ Jesus, and have no confidence in the flesh. 3:4 Though I might also have confidence in the flesh. If any other man thinketh that he hath whereof he might trust in the flesh, I more: 3:5 Circumcised the eighth day, of the stock of Israel, of the tribe of Benjamin, an Hebrew of the Hebrews; as touching the law, a Pharisee; 3:6 Concerning zeal, persecuting the church; touching the righteousness which is in the law, blameless. 3:7 But what things were gain to me, those I counted loss for Christ.
They of the Circumcision (Israelites) who Believed, were said to be those of their nation who worshipped God in the spirit; who did not rest in the mere fact that they were descendents of Abraham.
John 5:41 I receive not honour from men. 5:42 But I know you, that ye have not the love of God in you. 5:43 I am come in my Father's name, and ye receive me not: if another shall come in his own name, him ye will receive. 5:44 How can ye believe, which receive honour one of another, and seek not the honour that cometh from God only? 5:45 Do not think that I will accuse you to the Father: there is one that accuseth you, even Moses, in whom ye trust. 5:46 For had ye believed Moses, ye would have believed me: for he wrote of me. 5:47 But if ye believe not his writings, how shall ye believe my words?
John 8:37 I know that ye are Abraham's seed; but ye seek to kill me, because my word hath no place in you. 8:38 I speak that which I have seen with my Father: and ye do that which ye have seen with your father. 8:39 They answered and said unto him, Abraham is our father. Jesus saith unto them, If ye were Abraham's children, ye would do the works of Abraham. 8:40 But now ye seek to kill me, a man that hath told you the truth, which I have heard of God: this did not Abraham.
As seen in the above, such had also been the distinction between the two kinds of Isralites back when the issue had been keeping the Law.
Acts 7:51 Ye stiffnecked and uncircumcised in heart and ears, ye do always resist the Holy Ghost: as your fathers did, so do ye. 7:52 Which of the prophets have not your fathers persecuted? and they have slain them which shewed before of the coming of the Just One; of whom ye have been now the betrayers and murderers: 7:53 Who have received the law by the disposition of angels, and have not kept it.
The difference had been which of the two worshipped God in the spirit - that, is, not merely outwardly, as pleasing men (to impress one another) but as pleasing God.
Romans 2:17 Behold, thou art called a Jew, and restest in the law, and makest thy boast of God, 2:18 And knowest his will, and approvest the things that are more excellent, being instructed out of the law; 2:19 And art confident that thou thyself art a guide of the blind, a light of them which are in darkness, 2:20 An instructor of the foolish, a teacher of babes, which hast the form of knowledge and of the truth in the law. 2:21 Thou therefore which teachest another, teachest thou not thyself? thou that preachest a man should not steal, dost thou steal? 2:22 Thou that sayest a man should not commit adultery, dost thou commit adultery? thou that abhorrest idols, dost thou commit sacrilege? 2:23 Thou that makest thy boast of the law, through breaking the law dishonourest thou God? 2:24 For the name of God is blasphemed among the Gentiles through you, as it is written. 2:25 For circumcision verily profiteth, if thou keep the law: but if thou be a breaker of the law, thy circumcision is made uncircumcision.
2:28 For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh: 2:29 But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God.
Merely keeping the Law was not enough.
The heart attitude from within which a Jew kept the Law had also been an issue - as pleasing men, or God.
Note: In Romans 2, verses 26-27 are mentioned by Paul from within the context of the issue he is relating in Romans 1:18-3:20.
Philippians 3:1 Finally, my brethren, rejoice in the Lord. To write the same things to you, to me indeed is not grievous, but for you it is safe. 3:2 Beware of dogs, beware of evil workers, beware of the concision. 3:3 For we are the circumcision, which worship God in the spirit, and rejoice in Christ Jesus, and have no confidence in the flesh. 3:4 Though I might also have confidence in the flesh. If any other man thinketh that he hath whereof he might trust in the flesh, I more: 3:5 Circumcised the eighth day, of the stock of Israel, of the tribe of Benjamin, an Hebrew of the Hebrews; as touching the law, a Pharisee; 3:6 Concerning zeal, persecuting the church; touching the righteousness which is in the law, blameless. 3:7 But what things were gain to me, those I counted loss for Christ.
They of the Circumcision (Israelites) who Believed, were said to be those of their nation who worshipped God in the spirit; who did not rest in the mere fact that they were descendents of Abraham.
John 5:41 I receive not honour from men. 5:42 But I know you, that ye have not the love of God in you. 5:43 I am come in my Father's name, and ye receive me not: if another shall come in his own name, him ye will receive. 5:44 How can ye believe, which receive honour one of another, and seek not the honour that cometh from God only? 5:45 Do not think that I will accuse you to the Father: there is one that accuseth you, even Moses, in whom ye trust. 5:46 For had ye believed Moses, ye would have believed me: for he wrote of me. 5:47 But if ye believe not his writings, how shall ye believe my words?
John 8:37 I know that ye are Abraham's seed; but ye seek to kill me, because my word hath no place in you. 8:38 I speak that which I have seen with my Father: and ye do that which ye have seen with your father. 8:39 They answered and said unto him, Abraham is our father. Jesus saith unto them, If ye were Abraham's children, ye would do the works of Abraham. 8:40 But now ye seek to kill me, a man that hath told you the truth, which I have heard of God: this did not Abraham.
As seen in the above, such had also been the distinction between the two kinds of Isralites back when the issue had been keeping the Law.
Acts 7:51 Ye stiffnecked and uncircumcised in heart and ears, ye do always resist the Holy Ghost: as your fathers did, so do ye. 7:52 Which of the prophets have not your fathers persecuted? and they have slain them which shewed before of the coming of the Just One; of whom ye have been now the betrayers and murderers: 7:53 Who have received the law by the disposition of angels, and have not kept it.
The difference had been which of the two worshipped God in the spirit - that, is, not merely outwardly, as pleasing men (to impress one another) but as pleasing God.
Romans 2:17 Behold, thou art called a Jew, and restest in the law, and makest thy boast of God, 2:18 And knowest his will, and approvest the things that are more excellent, being instructed out of the law; 2:19 And art confident that thou thyself art a guide of the blind, a light of them which are in darkness, 2:20 An instructor of the foolish, a teacher of babes, which hast the form of knowledge and of the truth in the law. 2:21 Thou therefore which teachest another, teachest thou not thyself? thou that preachest a man should not steal, dost thou steal? 2:22 Thou that sayest a man should not commit adultery, dost thou commit adultery? thou that abhorrest idols, dost thou commit sacrilege? 2:23 Thou that makest thy boast of the law, through breaking the law dishonourest thou God? 2:24 For the name of God is blasphemed among the Gentiles through you, as it is written. 2:25 For circumcision verily profiteth, if thou keep the law: but if thou be a breaker of the law, thy circumcision is made uncircumcision.
2:28 For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh: 2:29 But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God.
Merely keeping the Law was not enough.
The heart attitude from within which a Jew kept the Law had also been an issue - as pleasing men, or God.
Note: In Romans 2, verses 26-27 are mentioned by Paul from within the context of the issue he is relating in Romans 1:18-3:20.