v1: Paul brings his personal example and testimony, not as a boast, but as an encouragement. He is full of joy for the Lord, and wants the Philippians to share that joy.
What he was writing required discernment and application; discernment in identifying those who taught a different message (as in v2-3), and application, so that they might obey God's words.
v2: Paul uses the words "dogs" to refer to those who oppose the things of Christ; see also Ex 11.7; Judg 7.5; 1 Kings 21; Ps 22.16, 20; Prov 26.11; Acts 20.29; Rev 22.15; at no point is there a commendation of such people. At that time, dogs were scavengers, detested in the wider culture, and considered unclean by the Jews.
The reference to mutilation is to those Judaizers, who have confidence in the flesh; they break down what is good, by insisting on submission to the Jewish law as the means of salvation, and they made the righteous sad. See Paul’s comments in Gal 5.12.
v3: The real circumcision, Christians, experiencing true separateness, Rom 2.29-30; 1 Cor 1.29; 2 Cor 6.17. They are characterised by true joy and true worship, but do not have confidence in the flesh.
The Jewish practice of circumcision related to the putting away of sin and the flesh, as in Josh 5. But even before circumcision was the principle of faith, see Rom 4.9-12; so Abraham was circumcised as a sign of his faith in God. The Jewish people had come to esteem the sign but miss the reality of faith.
v4: Before being converted to Christ, Paul had confidence in the flesh. Indeed, he had greater confidence in the flesh than anyone. He had experienced both false and true, and he knew the difference. Confidence in the flesh is here legalism, which is following man-made rules.
v5-6: Paul's confidence in the flesh. He had been circumcised, as all true Jews were. He belonged to Israel, but also to Benjamin; after the dispersion of the tribes in 2 Kings 17.6,18, only Judah and Levi remained, with very few of other tribes. It was therefore unusual for a Jew to trace his genealogy to another tribe; yet, some 750 years later, Paul could. It was important for a Jew to be able to trace his ancestry, see Matt 1; Luke 3. Doubtless this would have been more true for a Pharisee.
Paul excelled in works of legalism, so much so that he was regarded as faultless. He advanced in the Jewish religion, Acts 22.3; 26.5, and had been well-known amongst the Jewish people. His fame in persecuting the church was also known.
v7: "But", now things are different.
Since Christ now meant so much to Paul, those other things meant nothing, useless, loss. Here is the desire of the truly spiritual person; set your targets high, seek this same attitude. The things we learned from another religion are useless to us, they do not contribute to our understanding of Christ and His ways.
v8: Paul had not just rejected the old way, he had embraced something far better. Knowing Christ Jesus "my Lord" is everything. And for this, Paul happily suffered the loss of all things, that he might "gain" Christ - here is real profit!
v9: Christianity is about righteousness and that from God, not by the law, Rom 3.21-22. This is real security, righteousness from God.
v10-11: The desire and discipline necessary to pursue the highest of aims. Here is life on another level, knowing the power of His resurrection, Eph 1.19-20, bringing newness of life. We also share in His sufferings.
These things increasingly conform us to Him, as in v21, Rom 8.29. Now there is a growing conformity of character. In Heaven there will be conformity in nature, in form.
"Becoming like Him", Gk: SUMMORPHIZO, similar to the word "form" in 2.6-7; it refers to an inward spiritual transformation.
v12: Paul's humility, since he had not attained what he was aiming for. But he pressed on, full of spiritual ambition and desire for Christ.
Christ Jesus has laid hold of me, that I might be conformed. I must press on to seek that same conformity. See Eph 1.4; we are chosen in Him that we might be holy and blameless.
v13-14: Humility; Paul claimed not to have taken hold. Here is an answer to the teaching of perfectionism, as well as the error of idle complacency. Since we recognise that we fall short, we must press on seeking the Lord's will, and conformity to His character.
'We are to overcome and press on to God's purposes, forgetting what is behind and keep on going. The priority in our personal spiritual warfare is to overcome whatever circumstances we may find ourseles pulled down by.' (David Devenish, Demolishing Strongholds).
v15-16: The encouragement to press on together; we must share the attitude of pressing on to know Christ. We must help those who "think differently", and we all need a teachable spirit.
v17: Follow the godly example of others. Paul is bold here, asking others to note and to follow his example. Similarly, he tells the Philippians Christians to note those who live godly, and to follow that example also.
v18-19: Many, perhaps the majority, do not follow Paul's example and teaching; they are enemies of the cross of Christ, setting their desires and affections on worldly, physical things. It grieved Paul that although God has revealed the truth through Jesus Christ, many rejected Him, and taught their own religion.
For the natural, unspiritual man, his glory is in himself, and selfishly meeting his own desires. The Christian, in contrast, lives for the Lord (Rom 14.8; 2 Cor 5.15; Phil 1.20).
v20: Our citizenship is in Heaven. Our lives must reflect that, including looking forward to Christ's return. The implication is not that we belong to Heaven, not necessarily that that will be our eternal home. In the same way Paul, as a Roman citizen, would not expect to spend his whole life in Rome.
v21: The promise of a new body, conformed to His glorious body. He will do this because He is able to do it, fulfilling 1.6 and 2.13.This promise provides motivation for our striving to conformity with Christ.
'Jesus did not adorn himself with humanity to simply discard it. He adorned himself with humanity so that he might perfect humanity as our true priest.'
Patrick Schriener, The Ascension of Christ.