We are expected to grow beyond the basics. What are the basics? Repentance from dead works, faith in God, baptism, laying on of hands, resurrection and judgment. How do you get started in the Christian faith? By getting those things figured out.
Apparently, among those who genuinely believe, some grow up to be weeds and not genuine believers and are unable to be turned back. This is a sober warning for anyone playing games with the faith.
The promise of God's faithfulness and love in Hebrews 6:10 seems designed to comfort those who may be shaken by the warning in verses 1-9. If you are fully engaged, you have nothing to fear. God will be able to discern what is right. Have you done good to believers? Have you loved the only one who can save you? These questions are not questions about whether you've been religious, but about whether your heart has been changed.
The word of God is sure because nothing is greater than Him which can prevent Him from keeping it. He himself is our anchor and safe place. Jesus has broken through the veil into the presence of God (Hebrews 6:17-20).