The backslider says to himself/herself:
“I’m saved! Long ago I asked Jesus to come into my heart. It's just that I’m not living as a Christian right now. But I know that the LORD will overlook my life, because, after all, I’m pretty sure that I was really saved many years ago. Surely the LORD wouldn’t deny me heaven and send me to Hell just because I’ve failed at living the Christian life, would He? That would be so unfair if He forgot how I at least started the Christian life!”
The Lord Christ said long ago:
Enter through the narrow gate; for the gate is wide and the way is broad that leads to destruction, and there are many who enter through it. For the gate is small and the way is narrow that leads to life, and there are few who find it.
To the churches in the revelation, He also said this:
To him who overcomes, I will grant to eat of the tree of life which is in the Paradise of God.
He who overcomes will not be hurt by the second death.
To him who overcomes, to him I will give some of the hidden manna, and I will give him a white stone, and a new name written on the stone which no one knows but he who receives it.
He who overcomes, and he who keeps My deeds until the end, to him I will give authority over the nations …
He who overcomes will thus be clothed in white garments …
He who overcomes, I will make him a pillar in the temple of My God …
He who overcomes, I will grant to him to sit down with Me on My throne …
The Scriptures are very clear on this point: if you want to win, you must run and finish the entire race:
1 Cor 9.24-27
Do you not know that those who run in a race all run, but only one receives the prize? Run in such a way that you may win. Everyone who competes in the games exercises self-control in all things. They then do it to receive a perishable wreath, but we an imperishable. Therefore I run in such a way, as not without aim; I box in such a way, as not beating the air; but I discipline my body and make it my slave, so that, after I have preached to others, I myself will not be disqualified.
I present one last text to underscore that the backslider has no legitimate claim to heaven:
2 Cor 13.5
Test yourselves to see if you are in the faith; examine yourselves! Or do you not recognize this about yourselves, that Jesus Christ is in you—unless indeed you fail the test?
Backslider: you have been warned! Flee to the Lord Christ! Truly repent of your sins and by grace through faith call upon Jesus as LORD!