We might have a misunderstanding here.
I think you are saying that a demon can enter a true believer through sin.
There is not a single scripture to support your claim.
I believe a person can be posessed but not a true believer.
No one can judge anyone that profess Him on whethor or not they are a true believer or a true christian.
We are warned to beware of what and how we build on that foundation. Jesus had warned about suffering a thief to break through. That is applicable to those wayward believers that depart from faith, thinking they can receive the Holy Spirit again after a sign.
1 Timothy 4:1Now the Spirit speaketh expressly, that in the latter times some shall depart from the faith, giving heed to seducing spirits, and doctrines of devils; [SUP]
2 [/SUP]Speaking lies in hypocrisy; having their conscience seared with a hot iron;
Here is the prophesy that foretells that believers will depart from faith and thus be invaded to fall for them and after them.
Proverbs 25:[SUP]
26 [/SUP]A righteous man falling down before the wicked is as a troubled fountain, and a corrupt spring. [SUP]
27 [/SUP]It is not good to eat much honey: so for men to search their own glory is not glory. [SUP]
28 [/SUP]He that hath no rule over his own spirit is like a city that is broken down, and without walls.
And yet these wayward believers are still His, but unless they repent by looking to the Son to deliver them, they run the risk of being left behind as God will excommunicate those not found abiding in Him.... unless they repent before the Bridegroom comes.
But it is important to note that they are still brothers even though they no longer walk after the tradition taught of us and are disorderly.
Thessalonians 3:1Finally, brethren, pray for us, that the word of the Lord may have free course, and be glorified, even as it is with you: [SUP]
2 [/SUP]And that we may be delivered from unreasonable and wicked men: for all men have not faith. [SUP]
3 [/SUP]But the Lord is faithful, who shall stablish you, and keep you from evil. [SUP]
4 [/SUP]And we have confidence in the Lord touching you, that ye both do and will do the things which we command you. [SUP]
5 [/SUP]And the Lord direct your hearts into the love of God, and into the patient waiting for Christ. [SUP]
6 [/SUP]Now we command you, brethren, in the name of our Lord Jesus Christ, that ye withdraw yourselves from every brother that walketh disorderly, and not after the tradition which he received of us. [SUP]
7 [/SUP]For yourselves know how ye ought to follow us: for we behaved not ourselves disorderly among you;.......[SUP]
14 [/SUP]And if any man obey not our word by this epistle, note that man, and have no company with him, that he may be ashamed. [SUP]
15 [/SUP]Yet count him not as an enemy, but admonish him as a brother.
This reference was towards the apostasy mentioned earler in the previous chapter.
2 Thessalonians 2:[SUP]
9 [/SUP]Even him, whose coming is after the working of Satan with all power and signs and lying wonders, [SUP]
10 [/SUP]And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved. [SUP]
11 [/SUP]And for this cause God shall send them strong delusion, that they should believe a lie: [SUP]
12 [/SUP]That they all might be damned who believed not the truth, but had pleasure in unrighteousness.
That damnation being having been cut asunder to have their portion from the holy city and appointed with the unbelievers.
Paul reminds them of how we had receoved the promise of the Spirit at our salvation to reproving that apostasy mentioned above.
2 Thessalonians 2:[SUP]
13 [/SUP]But we are bound to give thanks alway to God for you, brethren beloved of the Lord, because God hath from the beginning chosen you to salvation through sanctification of the Spirit and belief of the truth: [SUP]
14 [/SUP]Whereunto he called you by our gospel, to the obtaining of the glory of our Lord Jesus Christ. [SUP]
15 [/SUP]Therefore, brethren, stand fast, and hold the traditions which ye have been taught, whether by word, or our epistle.
More proof that these prophesied believers falling away are still His:
John 10:1Verily, verily, I say unto you, He that entereth not by the door into the sheepfold, but climbeth up some other way, the same is a thief and a robber. [SUP]
2 [/SUP]But he that entereth in by the door is the shepherd of the sheep. [SUP]
3 [/SUP]To him the porter openeth; and the sheep hear his voice: and he calleth his own sheep by name, and leadeth them out. [SUP]
4 [/SUP]And when he putteth forth his own sheep, he goeth before them, and the sheep follow him: for they know his voice. [SUP]
5 [/SUP]And a stranger will they not follow, but will flee from him: for they know not the voice of strangers. [SUP]
6 [/SUP]This parable spake Jesus unto them: but they understood not what things they were which he spake unto them. [SUP]
7 [/SUP]Then said Jesus unto them again, Verily, verily, I say unto you, I am the door of the sheep. [SUP]
8 [/SUP]All that ever came before me are thieves and robbers: but the sheep did not hear them. [SUP]
9 [/SUP]I am the door:
So those believers that seek after receiving the Holy Spirit again after a sign of tongues that comes with no interpretation is the same as climbing up another way in approaching God the Father other than by way of the Son by asking the Spirit as if He can move on His own accord and be the One to ask for in getting tongues which comes with no interpretation that is an apt description of following after a stranger's voice as they continue to use that tongue as a prayer language, and thus coming before the Son as a thief, cutting inbetween us in our personal time of prayer with Him with babbling nonsense.
And yet they are His sheep even for following the stranger's voice as He says He MUST bring them as they will be MADE to hear His voice and be of the one fold and one shepherd.
John 10:[SUP]
14 [/SUP]I am the good shepherd, and know my sheep, and am known of mine. [SUP]
15 [/SUP]As the Father knoweth me, even so know I the Father: and I lay down my life for the sheep. [SUP]
16 [/SUP]
And other sheep I have, which are not of this fold:
them also I must bring, and they shall hear my voice; and there shall be one fold, and one shepherd.
So this is why we can never judge a believer as if he was never saved, but we can judge as in correcting a believer when they are not abiding in Him as we are to withdraw from unrepentant believers to admonish them as a brother & not as an enemy.