Partaker of heavenly calling

You might respond that this warning doesn't appy to me because I am saved. But the author addresses the "holy brethren, partakers of a heavenly calling" (Heb 3:1). "He is able to save forever those who draw near to God through Him" (7:25). You have "been enlightened and have tasted of the heavenly gift and have been made partakers of the Holy Spirit" (6:4). "Beloved, we are convinced of better things concerning you, and things that accompany salvation" (:9). Therefore they are Jewish believers. So why warn them about backsliding? Perhaps they are vulnerable because the New Covenant requires a different kind of faith than the Old Covenant.

Scripture should have been clear enough to them. "'He who beholds the Son and believes in Him will have eternal life'" (Jn 6:40). "'I give eternal life to them, and they will never perish; and no one will snatch them out of My hand'" (10:28). You would think that without science fiction sources to distract them they would take eternal life literally. Jesus promised, "'He who believes in Me will never thirst'" (6:32). It is a matter of trust, and when Hebrews was written, a number of people were still alive who had heard Jesus. He said "'the one who comes to Me, I will certainly not cast out'" (:37). "'All that [the Father] He has given Me I lose nothing, but raise it up on the last day'" (:39).

Maybe they missed the security of the religious routines of Tabernacle worship. But Jesus has become the New Covenant. "Christ was faithful as a Son over His house-whose house we are" (Heb 3:6). "Through Him we both have our access in the Spirit to the Father . . . and are of God's household" (Eph 2:18-19). Paul asks "who will separate us from the love of Christ?" (Ro 8:35). "For I am convinced that . . . [nothing] will be able to separate us from the love of God, which is in Christ Jesus our Lord" (:38-39).