This isn't a message of "perseverance" to Christians. This is a message to the Hebrews that if they reject the truth of the message of Christ to go back to their legalistic laws, there remains no longer a sacrifice for sin. The Law was swept away with Christ.
How can the elect of God, God's chosen people, reject the truth of the message of Christ? Or are some elect predestined to reject?
I disagree. Let's look at the verse more carefully and read what is there, not inserting your own theology into it:
For if we sin wilfully after we have received the knowledge of the truth, there remains no more sacrifice for sins...
Nothing about returning back to legalistic rituals - but to sin. Rituals are not sinful! God HIMSELF commanded them. The fact of the matter is that a person who willfully commits adultery, etc., is cutting themselves off from Christ's redemptive suffering. They are not in a "saved" status with the Lord.
Regards