Hebrews of losing their salvation (remember this is a reference to individual Jews in Israel, losing the opportunity to be a part of their promised Kingdom – their salvation); here are some verses to consider.
Hebrews 1:2 refers to the time as “these Last Days” which began in Acts 2:17. Hebrews 2:1-5 speaks about the gospel our Lord preached which was “the gospel of the Kingdom” and was the same the Apostles preached when the Holy Spirit came (in Acts 2) and Hebrews 2:5 says it concerns “the world to come, whereof we speak.”
The whole theme of the book of Hebrews is leaving the temple and sacrifices, which is what the Anti-Christ will reinstate during the 7 year tribulation. Hebrews 12:15-17 then warns of selling out as did Esau and loose out on the inheritance. Hebrews 10:1 says that the law is a shadow of “things to come.” Even the verse about “not forsaking the assembling of ourselves together” in Hebrews 10:25 goes on to say “so much the more, as ye see the day approaching.” “The Day” is a reference to “the Day of the Lord” in which comes the deception of the Anti-Christ. The “sinning willfully” of Hebrews 10:26-30 is a reference to the “mark of the Beast” which is to reject Jesus Christ and face “vengeance.” “Drawing back unto perdition” in Hebrews 10:29 speaks of any in Israel who claim to believe, but return to the temple, the sacrifice and the Anti-Christ system.
In the same respect, Hebrews 12:25-29 is a warning for those who reject Jesus Christ’s words from heaven (which is where Jesus Christ is when Hebrews was written, waiting to return in Judgment). Those who reject these warnings will not remain when He “shakes the Heavens and the Earth” – which is fulfilled in the book of Revelation. Lastly, in the book of Hebrews, the Jews are told to “come to Christ without the camp;” to leave the city (as in Matthew 24:15), because here they “have no continuing city, but seek one to come.”