GINOLJC, 100% correct, scripture, Romans 14:13 "Let us not therefore judge one another any more: but judge this rather, that no man put a stumblingblock or an occasion to fall in his brother's way".
Any one that believes in the Lord Jesus Christ and that God raised Him from the dead is saved, and thus an elect so no one can judge a professing believer as not a christian, thus condemning him as not saved when he is.
However, we are to "judge" as in "correct", not "condemn" but "correct" and even "rebuke" harshly if necessary when a christian have gone astray.
1 Timothy 5:20 Them that sin rebuke before all, that others also may fear.21 I charge thee before God, and the Lord Jesus Christ, and the elect angels, that thou observe these things without preferring one before another, doing nothing by partiality.
2 Timothy 4:1I charge thee therefore before God, and the Lord Jesus Christ, who shall judge the quick and the dead at his appearing and his kingdom;2 Preach the word; be instant in season, out of season; reprove, rebuke, exhort with all long suffering and doctrine.3 For the time will come when they will not endure sound doctrine; but after their own lusts shall they heap to themselves teachers, having itching ears;
Many will go astray and are in these latter days but even though they have fallen away from the faith, they are still considered as brothers.
2 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:2 And that we may be delivered from unreasonable and wicked men: for all men have not faith. 3 But the Lord is faithful, who shall stablish you, and keep you from evil. 4 And we have confidence in the Lord touching you, that ye both do and will do the things which we command you. 5 And the Lord direct your hearts into the love of God, and into the patient waiting for Christ. 6 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. 7 For yourselves know how ye ought to follow us: for we behaved not ourselves disorderly among you;..............14 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. 15 Yet count him not as an enemy, but admonish him as a brother.
So even a former believer is still saved, but he is still called by Him to repent by going before that throne of grace of help in freeing him from his unbelief and reproving the error that over threw his faith in Him to restore that fellowship with the Father & the Son and be ready to receive that eternal glory that comes with our salvation and that is to be a vessel unto honor in His House at the Marriage Supper table.
2 Timothy 2:10 Therefore I endure all things for the elect's sakes, that they may also obtain the salvation which is in Christ Jesus with eternal glory. 11 It is a faithful saying: For if we be dead with him, we shall also live with him: 12 If we suffer, we shall also reign with him: if we deny him, he also will deny us: 13 If we believe not, yet he abideth faithful: he cannot deny himself.
18 Who concerning the truth have erred, saying that the resurrection is past already; and overthrow the faith of some. 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.
So look to Jesus Christ and point the believers that are astray to Jesus Christ for the help they need to discern the truth & repent by.
James 1:5 If any of you lack wisdom, let him ask of God, that giveth to all men liberally, and upbraideth not; and it shall be given him.
Hebrews 4:12 For the word of God is quick, and powerful, and sharper than any twoedged sword, piercing even to the dividing asunder of soul and spirit, and of the joints and marrow, and is a discerner of the thoughts and intents of the heart. 13 Neither is there any creature that is not manifest in his sight: but all things are naked and opened unto the eyes of him with whom we have to do. 14 Seeing then that we have a great high priest, that is passed into the heavens, Jesus the Son of God, let us hold fast our profession. 15 For we have not an high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as we are, yet without sin. 16 Let us therefore come boldly unto the throne of grace, that we may obtain mercy, and find grace to help in time of need.
We are not to condemn any professing believer or even a former believer that they are not a christian or they never were or that they are not saved. We are to correct one another in love when we have gone astray or have fallen away from the faith or have departed from the traditions taught of us, and withdraw from unrepentant believers & former believers to admonish them as still brothers.