Bible teachers explain that our position in Christ is based upon the foundation of the scriptures. However, each believer didn't have his own personal Bible like we do today. But the author of Hebrews reminded them "to give the more earnest heed to the things which we have heard" (Heb 2:2 KJV). Those Jews had been taught weekly on the Sabbath about the Old Covenant. Those "things" included "the man who finds wisdom and the man who finds understanding" (Proverbs 3:13). "The Lord by wisdom founded the earth, by understanding He established the heavens. By His knowledge the deeps were broken up" (:19-20). Hebrews was warning them not to "drift away" but to keep focused. "Let them not vanish from your sight; keep sound wisdom and knowledge" (:21).
Hebrews urges them to persevere. "Solid food is for the mature, who because of practice have their senses trained" (Heb 5:14). "Therefore leaving the elementary teaching about Christ, let us press on to maturity" (6:1). They must have known "in Him you have been made complete" (Col 2:10) and that "He made you alive together with "Him" (:13). "Having also believed, you were sealed in Him with the Holy Spirit of promise, who is given as a pledge of our inheritance (Eph 11:13-14) and "by whom you were sealed for the day of redemption" (4:30). They should have put their eyes on the future and not be returning to the past which would represent apostasy. "By this will we have been sanctified through the offering of the body of Jesus Christ once for all" (Heb 10:10). "For by one offering He has perfected for all time those who are sanctified" (:14). Hebrews is warning them not to reject the Gospel. "In later times some will fall away from the faith" (1Ti 4:1) but the day of the Lord "will not come unless the apostasy comes first" (2Ti 2:3). "How much severer punishment do you think he will deserve who has trampled under foot the Son of God . . . by which he was sanctified?" (Heb 10:29).