Yes, key point is that they are His sheep on the basis of faith in Him. And all believers possess eternal life. And therefore, will never perish. John 10:28
A couple of points:
1. The Bible never says that Jesus gives eternal life to "all who are in Him and He in them". In fact, it doesn't even say "all who are in Him".
Eph 1:13 tells us plainly that those having believed are sealed IN HIM with the Holy Spirit. So, the WAY one becomes "in Him" is by having believed.
The tense (aorist) shows that there is no requirement for "as long as they stand grounded".
1. The Bible has NO verses with the condition of "as long as..." for salvation.
Never perish = those in Christ and He in them at His coming as they stand grounded in faith
v.28 says no such thing. It says He gives them (believers: John 3:15,16,36, 5:24, 6:47, 11:25-27) eternal life and they SHALL NEVER PERISH.
v.38 says "neither things present nor things to come (future)". Know what that means? It means REGARDLESS of what occurs in the future, the believer remains secure.
Of course one IS SAVED WHEN they believe. Your comment suggests that the believer is not yet saved. Where does the Bible make such a statement or suggestion??
Check the context. "to the end" specifically refers to the 7 year period called the Tribulation. This verse has no relevance to us today.
Yes, Rom 8:38 tells us that "neither things present nor things future" will separate us from God's love. And the believer is sealed with the Holy Spirit as a guarantee for the day of redemption (Eph 1:13,14) on the basis of HAVING BELIEVED (aorist tense).
Faith is Christ Jesus in whom we believe. If we quit believing we are no longer going to be given eternal life, but only that of damnation when Christ comes and calls all (saint and sinner) from their grave, John 5:28, 29.
Jesus gives eternal life to all who will believe in Him as He is our faith in whom we believe in.
2 Corinthians 5:17 Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new.
John 15: 4 Abide in me, and I in you. As the branch cannot bear fruit of itself, except it abide in the vine; no more can ye, except ye abide in me. 5 I am the vine, ye are the branches: He that abideth in me, and I in him, the same bringeth forth much fruit: for without me ye can do nothing. 6 If a man abide not in me, he is cast forth as a branch, and is withered; and men gather them, and cast them into the fire, and they are burned.
John 10: 26 But ye believe not, because ye are not of my sheep, as I said unto you. 27 My sheep hear my voice, and I know them, and they follow me: 28 And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand.
1 John 2:23 Whosoever denieth the Son, the same hath not the Father: (but) he that acknowledgeth the Son hath the Father also. 24 Let that therefore abide in you, which ye have heard from the beginning. If that which ye have heard from the beginning shall remain in you, ye also shall continue in the Son, and in the Father. 25 And this is the promise that he hath promised us, even eternal life.
Ephesians 1:13 In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise
We are sealed by the Holy Spirit of promise as that promise is eternal life to all who by faith believe in Christ. Many have walked away from faith and no longer believe so they have not the promise anymore.
Colossians 1:23 If ye continue in the faith grounded and settled, and be not moved away from the hope of the gospel, which ye have heard, and which was preached to every creature which is under heaven; whereof I Paul am made a minister;
Faith is the requirement as long as we are not moved away from the hope of the gospel.
Go back to Ephesians 1:13 we are only sealed by the Holy Spirit of promise, but yet not saved as we have to endure all things until the end when Christ returns and then we are saved, Matthew 24:13 But he that shall endure unto the end, the same shall be saved.
Matthew 24:12, 13 to endure until the end means enduring everything from now today through that of the seventh trumpets and seven vial judgements as then the end will come when Christ returns on the last day after the tribulations that will take place in the world, John 6:40; John 5:28, 29. There is no pretrib rapture as all who are alive during the seven trumpets sounding and the seven vial judgements are sealed by the holy Spirit of promise that Gods wrath will not touch those who are His own and when all is finished the old heaven and earth will have passed away and a new heaven and earth will become new again and New Jerusalem will be ushered down from heaven and we who have endured will then have eternal life with the Father.