As I've explained to you in other threads, the Scriptures I cited don't refer to "false Christians" but to Christian brethren, identified repeatedly as such in the various passages. 1 Corinthians 3 is a great example.
1 Corinthians 3:1-3
1 And I, brethren, could not speak unto you as unto spiritual, but as unto carnal, even as unto babes in Christ.
2 I have fed you with milk, and not with meat: for hitherto you were not able to bear it, neither yet now are you able.
3 For you are yet carnal: for whereas there is among you envying, and strife, and divisions, are you not carnal, and walk as men?
Paul begins in this passage by identifying his audience as "brethren." Not "false brethren." Then Paul continues, describing his "brethren" as "carnal" but ALSO "babes in Christ." The "brethren" were both carnal and in Christ, not carnal and therefore false brethren who could not, as such, be in Christ. The brethren were so "babyish" spiritually that Paul could only feed them spiritual "milk" not "meat." Nonetheless, Paul identified these people as brethren and confirmed that they were in Christ.
1 Corinthians 3:9
9 ...you are God's field, God's building.
Here, six verses later in chapter 3, Paul described his readers as "God's field" and "building," not "false brethren," not "false Christians," but fellow born-again believers, the possessions of God. Doing so, Paul established further that it was possible for born-again people to be spiritually-immature, carnal, divisive and partisan, and still be genuine children of God.
1 Corinthians 3:13-15
13 Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is.
14 If any man's work abide which he has built thereupon, he shall receive a reward.
15 If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
In this section of chapter 3, Paul indicated that a believer's "work" can be entirely unacceptable to God, revealed as "wood, hay and stubble" by His testing and destroyed. But the believer remains saved, regardless! So poor has the "work" of their building been that God has burned it up but though they suffer the loss of His rewards, they are saved (though with the smoke of hellfire on their clothing).
1 Corinthians 3:16-17
16 Do you not know that you are a temple of God and that the Spirit of God dwells in you?
17 If any man destroys the temple of God, God will destroy him, for the temple of God is holy, and that is what you are.
Paul adds another confirmation of the membership of his readers in God's family here, saying that the carnal babes in Christ, his brethren, and fellow fields and buildings of God, were also "temples of God," indwelt by the Spirit of God, and holy temples of God. This he says of those whom he had described at the beginning of the chapter as follows:
1 Corinthians 3:3
3 for you are still fleshly. For since there is jealousy and strife among you, are you not fleshly, and are you not walking like mere men?
Clearly, Paul did NOT hold to a sinless perfection view of the born-again believer.
1 Corinthians 3:21-23
21 So then let no one boast in men. For all things belong to you,
22 whether Paul or Apollos or Cephas or the world or life or death or things present or things to come; all things belong to you,
23 and you belong to Christ; and Christ belongs to God.
Coming full circle to his remarks at the beginning of the chapter, Paul reminds the believers at Corinth here, his brethren, fellow fields, buildings, and holy temples of God, that they ought not to boast in men but to remember that they belonged to Christ who belongs to God. There is simply no way a person can read this chapter honestly and naturally and not understand what I've taken pains to point out from the chapter. It's right there on the surface of Paul's words, plain as day: Christians are not sinlessly perfect.