I've determined that for me the most important thing to remember when reading the book of Hebrews is that it is addressed to a group of messianic Jews who are at risk of losing their faith, and it often sounds like the author means their salvation, because of the persecution they are currently experiencing. I have sat on both sides of the eternal security versus conditional security argument and believe in eternal security except . . .
I grew up under the Pentecostal teaching of conditional security but attended Baptist school and a couple of Baptist churches that taught eternal security. My current understanding of the book of Hebrews makes me lean towards the conditional security argument, especially one line in the book, which is a big problem for me. That verse says that having once fallen away you can't return, and I don't see how that statement can be true.
Personally, I’m okay saying this, because my salvation isn't dependent on me understanding every verse in the Bible. Believing I have to understand everything would mean that God had nothing more to teach me, nothing more to show me in the Bible, and we all know that's not true. So I will not be teaching on eternal or conditional security any time soon. What I will focus on is the all-sufficiency of Christ and the necessity of faith in every part of our lives. Or at least that's what I'd talk about if I were to teach on Hebrews today.