Christians Striving for Perfection by God's Grace
Although Christians while in the flesh by God's grace can resist sin and have power over it (Titus 2:11-15) BUT they cannot reach the state of sinless perfection because they are still in the flesh and the old man (the flesh) is still alive as even the best of apostles like Paul still struggled with sin (Romans 7:20). So what is the command for perfection for believers? Romans 7:1 says, "Having therefore these promises dearly beloved let us cleanse ourselves from all filthiness of the flesh and spirit, perfecting holiness in the fear of God." Please note that this message is about perfection, NOT SALVATION. 1 John 1:8 says, "For if we say we have so sin then the truth is not in us." Christians strive to be perfect because they are saved not to stay saved or to be saved!
So how does this perfection work? Perhaps a picture would be like the olive oil. In the Old Testament, God commanded in Exodus 27:20 saying, "And thou shalt command the children of Israel, that they bring thee pure oil olive beaten for the light, to cause the lamp to burn always." Olive oil is always produced by beating olives and no beating, no oil. Pressing happens and the olive oil is extracted from the olives themselves. If the olive oil had impurities, the lamps will not burn properly and the temple walls were filled with soot. God always demanded the best because He is a holy and righteous God. Likewise, Christians undergo trials in order to remove the impurities so they can burn bright. It can be co-related to Matthew 5:16 saying, "Let your light shine so before men that they may see your good works and glorify your Father which is in Heaven."
God has already prepared good works for the Christian to do which includes preaching against false religions and telling them about His Son the Lord Jesus Christ. Preaching is NEVER effective unless if it is accompanied by good works to show one's faith. Salvation is received by faith and puts a person into Christ then good works inevitably comes out. That's the whole message of Ephesians 2:8-10- saved not by works and doing good works because one is saved NOT to stay saved or to be saved. And here's what- when Christians do sin, God will not cast them out BUT He has prepared that belt of truth to spank them because if they endure not chastising therefore they are outsiders and not His own (Hebrews 12:5-6). In total, Philippians 2:12-15 talks about working out salvation (NOT working on) as a result of God working in the Christian that they would be blameless and harmless, good children of God and a glorious example.