Summary: How do you know you a true believer of Christ or you are one of those who Jesus talked about in Matthew 7:21-23 "Not everyone who says to me, ’Lord, Lord,’ will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven. [2
1. True Believers Rejoices in the Lord verse 1a
Finally, my brothers, rejoice in the Lord!
The joy of which Paul writes is not the same as happiness. Because happiness as we know is temporal and depends upon favorable events. The angels who announced Jesus birth to the shepherds said in
Luke 2:10-11 But the angel said to them, "Do not be afraid. I bring you good news of great joy that will be for all the people.  Today in the town of David a Savior has been born to you; he is Christ the Lord.
Jesus said in John 15:11 I have told you this so that my joy may be in you and that your joy may be complete. Furthermore, John 17:13 "I am coming to you now, but I say these things while I am still in the world, so that they may have the full measure of my joy within them.
Luke 10:20 However, do not rejoice that the spirits submit to you, but rejoice that your names are written in heaven."
When is it hard for you to have joy? For me when I am under trial. Because my happiness relies on circumstances. If it goes my way I’m happy, if it doesn’t I am unhappy. But the Bible tells us in
James 1:2 Consider it pure joy, my brothers, whenever you face trials of many kinds,
1 Peter 4:12-13 Dear friends, do not be surprised at the painful trial you are suffering, as though something strange were happening to you.  But rejoice that you participate in the sufferings of Christ, so that you may be overjoyed when his glory is revealed.
2. True Believers Exercises Discernment verse 1b-2
It is no trouble for me to write the same things to you again, and it is a safeguard for you. Watch out for those dogs, those men who do evil, those mutilators of the flesh.
Paul here tells us the true believers exercises discernment: truth from error, good from evil. The apostle has warned the believers at Philippi before (1:27-28), but now he warns them again. The word safeguard (asphales) literally means (not to trip, stumble, or be overthrown). In Acts 20:31 So be on your guard! Remember that for three years I never stopped warning each of you night and day with tears.
Paul in verse 2 describes the false teachers as
Dogs - refers to wild scavengers, who roamed in groups feeding on garbage and occasionally attacking humans. He warns the Philippians to beware of those who call others dogs, but in reality dogs themselves who are unclean, filthy, vicious, and dangerous. To illustrate this better, this dogs (false teachers) followed Paul in his preaching ministry barking their false doctrine. Jesus tells us in Matt 7:15 "Watch out for false prophets. They come to you in sheep’s clothing, but inwardly they are ferocious wolves. Acts 20:29 I know that after I leave, savage wolves will come in among you and will not spare the flock. 2 John 1:9-11 Anyone who runs ahead and does not continue in the teaching of Christ does not have God; whoever continues in the teaching has both the Father and the Son.  If anyone comes to you and does not bring this teaching, do not take him into your house or welcome him.  Anyone who welcomes him shares in his wicked work.
Evil Workers – These men taught that the sinner was saved by faith plus good works. But Paul from his own life (v5-6) tells us that his and their good works are really evil works because they are done by the flesh. Titus 3:3-7 At one time we too were foolish, disobedient, deceived and enslaved by all kinds of passions and pleasures. We lived in malice and envy, being hated and hating one another.  But when the kindness and love of God our Savior appeared,  he saved us, not because of righteous things we had done, but because of his mercy. He saved us through the washing of rebirth and renewal by the Holy Spirit,  whom he poured out on us generously through Jesus Christ our Savior,  so that, having been justified by his grace, we might become heirs having the hope of eternal life.
False Circumcision – Here Paul describes the Judaizers (Jewish legalist who denies the gospel of grace and teaching that circumcision and keeping the law of Moses were necessary for salvation). This people prided themselves of being physically circumcise but not spiritually.
3. True Believers Worship in the Spirit v3a
For it is we who are the circumcision, we who worship by the Spirit of God,
Speaking to the Samaritan woman in John 4, Jesus clearly defined trued and acceptable worship. Shocked by His omniscient of her sinful life (v16-18), she tried to change the subject (v19-20), in response Jesus declared in verse 21 "Believe me, woman, a time is coming when you will worship the Father neither on this mountain nor in Jerusalem. True worship takes place in the heart, not a sacred location. Verse 22 tells us that acceptable worship is based on the truths revealed in Scriptures. Finally, verse 23-24 Jesus gives us the clearest definition of worship in all scriptures Yet a time is coming and has now come when the true worshipers will worship the Father in spirit and truth, for they are the kind of worshipers the Father seeks.  God is spirit, and his worshipers must worship in spirit and in truth."