And yet you insisted at first that a Christian cannot sin. You said -
"1 John 3:7-10
7 Dear children, do not let anyone lead you astray. He who does what is right is righteous, just as he is righteous. 8 He who does what is sinful is of the devil, because the devil has been sinning from the beginning. The reason the Son of God appeared was to destroy the devil's work. 9 No one who is born of God will continue to sin, because God's seed remains in him; he cannot go on sinning, because he has been born of God. 10 This is how we know who the children of God are and who the children of the devil are: Anyone who does not do what is right is not a child of God; nor is anyone who does not love his brother.
NIV
It is the ungodly world that is under the devil's power -- those who live under the control of the flesh, the world and their evil father; not Christ's Church! How long have you been an admirer of the devil? And notice that v. 8b is not in the future tense, as you claim by your earthly millennial kingdom nonsense. John did not teach that Christ will appear to destroy the devils' work -- but rather that He HAS APPEARED, i.e. his first advent!"
Now you seem to be back-tracking to Christians won't 'finally succumb to the devil's attacks into apostasy, but the devil will nevertheless be able to tempt and overcome Christians for a season.