You write,' no one reaches moral perfection in this life. Phil 3:12'.Here is how I analyze the problem:
No one achieves moral perfection in this life (Phil. 3:12), but no one who lacks divine love will reap eternal life with God (Gal. 6:7-8). Thus, a person who claims to be godly but who is behaving in an ungodly (unloving, untruthful) manner may be in one of the following categories:
a. a normally loving person observed during a rare moment when he/she acted uncharacteristically (Phil. 3:12-16),
b. an immature Believer, who is making progress–you should have known him/her a year ago! (1Cor. 3:1-3, Eph. 4:11-15)
c. a truthseeker who has not yet learned the correct interpretation of God’s Word (1Cor. 6:9-11, Eph. 5:8-9),
d. a back-slider or prodigal Christian, who has yet to learn by painful experience the value of learning to cooperate with God’s will.
e. a pseudo-Christian (Matt. 7:21, 1John 2:19), who may affirm morality while rejecting its divine rationale.
f. an apostate (Heb. 6:4-6, 10:23-39), who once believed but became blasphemous or foolish and ship-wrecked their faith (1Tim. 1:19-20), becoming completely corrupt and callous (Matt. 13:14-15, Heb. 6:4-6).
Paul listed some sins he implied genuine Christians would not typically commit (in 1Cor. 6:9-10), saying: “Do you not know that the wicked will not inherit the kingdom of God? Do not be deceived, neither the sexually immoral nor idolaters nor adulterers nor male prostitutes nor homosexual offenders nor thieves nor the greedy nor drunkards nor slanderers nor swindlers will inherit the kingdom of God.”
Apparently, although a new Christian might commit such sins occasionally, it is inconceivable (because antithetical to NT teaching) that a mature Christian would commit them so typically that the person could be classified as an adulterer, for example (1John 3:6). Back-sliding is the opposite of standing firm or persevering. Atheists might try to practice the “Golden Rule”, but the key issue for them on judgment day will be explaining what good reason they had for rejecting God rather than glorifying Him as the One who determines what is good/golden.
Sinners can overcome selfishness only by becoming one with Christ via faith in Him/God as Lord and thereby sharing His goodness because of union with His/God’s Holy Spirit. This spiritual union is denoted by references to those who have saving faith as children of God the Father (Rom. 8:14-16). This is why Christianity is a relationship with God motivated by gratitude for God’s grace (Psa. 100, Eph. 2:4-8) rather than a legalistic religion of working to merit God’s mercy because of fear of punishment.
However, Paul writes in verse 15 of that chapter,' Let us therefore, as many as are perfect, have this attitude.....'.
This shows that there is a 'perfection' attainable in this life. Paul includes himself as 'perfect' by using the word 'us'.
Is Paul contradicting himself by saying he is not perfect in v 12, and then saying he is in v15 ?.
The answer is no. He is talking about two different perfections. In v12, Paul is talking about absolute resurrection perfection that one attains in Heaven. The perfection in v15 is the perfection that Jesus mentioned when He called us 'to be perfect as your heavenly Father is perfect'. The context of Jesus' command is love. We are to be perfect in love. Having our hearts so filled with God's love that sin is dispelled. A pure heart. A holy heart.