John would disagree with you. "If we say that we have fellowship with Him, and walk in darkness, we lie and do not practice the truth." John was direct and to the point in I John.
John would not disagree with this: Those "lost" are still a true child of God even when left behind for not departing from iniquity before the Bridegroom comes.
John was addressing an erroneous belief among Christians that sin was no longer sin to them when they do it for why he referred to how Jesus walked in the light and there was no darkness at all as we are to do with His help to have fellowship with the Father & the Son.
"Now by this we know that we know Him, if we keep His commandments. 4 He who says, “I know Him,” and does not keep His commandments, is a liar, and the truth is not in him. 5 But whoever keeps His word, truly the love of God [
a]is perfected in him. By this we know that we are in Him. 6 He who says he abides in Him ought himself also to walk just as He walked."
"28 And now, little children, abide in Him, that [
h]when He appears, we may have confidence and not be ashamed before Him at His coming. 29 If you know that He is righteous, you know that everyone who practices righteousness is born of Him."
I would read that as saying that if they do not practice righteousness, they are not born of Him.
Then heed all of John's words. He was not talking about a believer can never sin, but that they should not live in unrepentant sinful lifestyle.
1 John 2:1My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous: 2 And he is the propitiation for our sins: and not for ours only, but also for the sins of the whole world. 3 And hereby we do know that we know him, if we keep his commandments. 4 He that saith, I know him, and keepeth not his commandments, is a liar, and the truth is not in him. 5 But whoso keepeth his word, in him verily is the love of God perfected: hereby know we that we are in him.
If any believer sin, "fall of the wagon", that would be consider as practicing unrighteousness but that does not mean he is not born of Him. John was emphasizing & exhorting believers to practice righteousness as a witness of abiding in Him as born of Him. The point is to call believers to repentance by going before that throne of grace for forgiveness and help not to do that again.
John is talking about discipleship; not salvation. Discipleship as in running that race is about abiding in Him daily by His grace & by His help.
John wanted to expose those that were walking in darkness as not abiding in Him as His disciples to warn others away from following them.
They will need His help daily to run that race as Paul had written below.
Hebrews 12:1Wherefore seeing we also are compassed about with so great a cloud of witnesses,
let us lay aside every weight, and the sin which doth so easily beset us, and let us run with patience the race that is set before us, 2 Looking unto Jesus the author and finisher of our faith; who for the joy that was set before him endured the cross, despising the shame, and is set down at the right hand of the throne of God.
Ephesians 1 says that God chose us beforehand to the adoption of children, THROUGH CHRIST. So if they do not depart iniquity, then they are not practicing righteousness, which means that they are not born of Christ. If they are not born of Him, then they were not ordained to the adoption of children, which means that they have no inheritance in Christ. (Also found in Ephesians.) There are other things they do not have as well.
it is true that they will not inherit the eternal glory that comes with our salvation in Christ Jesus which is to be that vessel unto honor in His House, but if they depart from iniquity with His help before the Bridegroom comes, they will be received by the Bridegroom as vessels unto honor. Those that do not depart from iniquity will be of the other vessels, the vessels unto dishonor, the vessels of wood & earth, BUT still in His House as they will be resurrected after the great tribulation to serve the King of kings on earth.
2 Timothy 2:19
Nevertheless the foundation of God standeth sure, having this seal, The Lord knoweth them that are his. And, let every one that nameth the name of Christ depart from iniquity.
20 But in a great house there are not only vessels of gold and of silver, but also of wood and of earth; and some to honour, and some to dishonour. 21 If a man therefore purge himself from these, he shall be a vessel unto honour, sanctified, and meet for the master's use, and prepared unto every good work.
The day of Christ Jesus is the day that people are left behind or not left behind. The good work is completed in that day. There is nothing that comes after. Only true believers who follow Christ are His children. Consider what Hebrews says
"4 For
it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit, 5 and have tasted the good word of God and the powers of the age to come, 6 [
c]if they fall away, to renew them again to repentance, since they crucify again for themselves the Son of God, and put
Him to an open shame.
7 For the earth which drinks in the rain that often comes upon it, and bears herbs useful for those by whom it is cultivated, receives blessing from God; 8 but if it bears thorns and briers,
it is rejected and near to being cursed, whose end
is to be burned.".
That errant application has been circling a lot in Christianity but they do so out of context.
Hebrews 6:1
Therefore leaving the principles of the doctrine of Christ, let us go on unto perfection; not laying again the foundation of repentance from dead works, and of faith toward God, 2 Of the doctrine of baptisms, and of laying on of hands, and of resurrection of the dead, and of eternal judgment. 3 And this will we do, if God permit.
Paul begins about after going through everything at conversion, they will not need to do that again for why they are to go on to perfection and explains why if you see the word
"For" at the beginning of verse 4 as meaning
"Because.." you might see the message intended with His help.
4 For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, 5 And have tasted the good word of God, and the powers of the world to come, 6 If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.
7 For the earth which drinketh in the rain that cometh oft upon it, and bringeth forth herbs meet for them by whom it is dressed, receiveth blessing from God: 8 But that which beareth thorns and briers is rejected, and is nigh unto cursing; whose end is to be burned.
Now think of verse 7 like what the earth did with the rain as the same thing as what a believer built on that foundation. If the believer built wood, stubble, and hay, it will get burned up in that day of verse 13 but the foundation remains and thus salvation remains verse 15, but at the cost of incurring physical death per verses 16-17 which will happen to those that get left behind for being in unrepentant iniquity.
1 Corinthians 3:10 According to the grace of God which is given unto me, as a wise masterbuilder, I have laid the foundation, and another buildeth thereon
. But let every man take heed how he buildeth thereupon. 11 For other foundation can no man lay than that is laid, which is Jesus Christ. 12 Now if any man build upon this foundation gold, silver, precious stones, wood, hay, stubble;
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 hath 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. 16 Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you? 17 If any man defile the temple of God, him shall God destroy; for the temple of God is holy, which temple ye are.
See the parallel? That is why it is impossible because they are still saved for why the call is to move on to perfection by repentance.