It has been my observation that those who choose to 'reject' their salvation do so based on lies.
Lies that they are told about Who God is; about His character; about the realities of Christ and His Work; about what will happen if they don't do thus-and-so; lies about what will happen if they DO do thus-and-so. Lies about Grace and Law. Lies that turn believers into neurotic, unstable messes who are exhausted in their insecurity and simply say, 'enough'.
It is my opinion that folks who 'reject' their salvation do so because of lies they've believed about that salvation and about God. But it's not the real salvation or the Real God they've rejected - they reject the counterfeits of God and His salvation that LIES have convinced them of.
If my husband came to me and told me he had heard this that and the other about me and wanted a divorce, I would not consent, because his decision would be based on lies. I would do everything I could do to show him what was true.
The Enemy, once someone comes to Christ, knows that that person is out of his reach. His goal from that point is to make that believer UNFRUITFUL, so that they cannot bring others into a saving relationship with God. So he lies, lies, lies about the salvation they have and about the steadfast faithfulness and goodness of God. If the Enemy cannot steal them away from God, neutralizing them is the next best thing in his book.
God, on the other hand, in His Word and through His Body, proclaims Truth. He proclaims the Truth of His love, mercy, grace, and faithfulness in Christ. The Scriptures tell us that when we believe in Christ, He comes to live in us. And He cannot deny Himself.
-JGIG