No one who is born again will be lost again. Christ changes the believer into a new creation, we cannot go back to the old again.
He gives us what we want when we trust in Him, that is to be changed forever.
Those who walk away after claiming to be Christians were never changed by Christ or they would not have gone back.
2 Corinthians 5:17 "Therefore if anyone is in Christ, this person is a new creation; the old things passed away; behold, new things have come."
1 John 2:19-20 "19They went out from us, but they did not belong to us. For if they had belonged to us, they would have remained with us. But their departure made it clear that none of them belonged to us. 20You, however, have an anointing from the Holy One, and all of you know the truth.…"
Hebrews 12:5-7 "…5And you have forgotten the exhortation that addresses you as sons: “My son, do not take lightly the discipline of the Lord, and do not lose heart when He rebukes you. 6For the Lord disciplines the one He loves, and He chastises every son He receives.” 7Endure suffering as discipline; God is treating you as sons. For what son is not disciplined by his father?…"
God never throws away those He has changed, their Spirit is changed but their body is still sinful and must be battled daily.
Galatians 5:16-18 "16 So I say, walk by the Spirit, and you will not gratify the desires of the flesh. 17 For the flesh craves what is contrary to the Spirit, and the Spirit what is contrary to the flesh. They are opposed to each other, so that you do not do what you want. 18 But if you are led by the Spirit, you are not under the law.…"
1 Corinthians 3:14-16 "…14 If what he has built survives, he will receive a reward. 15If it is burned up, he will suffer loss. He himself will be saved, but only as if through the flames. 16 Do you not know that you yourselves are God’s temple, and that God’s Spirit dwells in you?…"
The Holy Spirit does not hop in and out of those who are children of God.
2 Corinthians 1:21-22 "…21 Now it is God who establishes both us and you in Christ. He anointed us, 22 placed His seal on us, and put His Spirit in our hearts as a pledge of what is to come."
God never breaks His promises to us!
If we sin as believers He disciplines us until we confess to be cleansed. If we refuse then we miss the many blessings of walking with Christ and His Holy Spirit will go silent, He will not speak to those who will not listen to Him.
1 Thessalonians 5:19-22
"19 Do not quench the Spirit, 20 do not utterly reject [a]prophecies, 21 but examine everything; hold firmly to that which is good, 22 abstain from every form of evil."
The prophecies here are not new future telling or new revelations, they are the principles and prophecies already written in the Word of God. When a believer ignores the teachings of God in the Bible they will miss many blessings and rewards in heaven.
Since our salvation is not based on any good works we do keeping our salvation is not based on what we do, it is based on Christ Who lives in us. However, this is not a license to sin. Those who sin while born again are not blessed or content, they live in contiual guilt until they confess to be cleansed as God said they should in 1 John 1:9 written to believers.
1 John 1:9
"9 If we confess our sins, He is faithful and righteous, so that He will forgive us our sins and cleanse us from all unrighteousness."
Confessing sin for the non-believer does not save them unless they place their trust in Christ for paying their penalty for their sin.