What does Hebrews 10:27 mean?

The prior verse warned about a situation in which there was no longer a sacrifice for sins. This was framed in the context of those who have received the truth, but have persisted in some level of sin. Depending on how this passage is understood, this is either a reference to saved Christians mired in doubt and faithlessness, or those who never fully accepted the truth and instead rejected the gospel. The context surrounding this passage most strongly supports the first view.

Here, the writer warns about fear, judgment, fire, and fury. In the context of saved believers, this is not dissimilar from comments made earlier (Hebrews 6:7–8). Israel failed to "hold fast" to their faith in the wilderness (Hebrews 3:12–19), and Christians are warned not to make the same mistake (Hebrews 4:11). Those who do can expect judgment, pictured using the symbolism of fire. God often rendered earthly judgment against His chosen people in response to their sin (Numbers 14; Judges 2:1–5; Lamentations 1:4–5). Given this background, it's not unreasonable to interpret this warning as one given to saved Christians about the dire consequences of their own sins. The language used later in this same warning also leans heavily in favor of it being directed toward those who are saved (Hebrews 10:29).

Though the context does not support it as well, this passage has sometimes been understood as a warning to those who "almost" accept the gospel. In other words, those who are given a full, complete, and thorough opportunity to submit to Christ, yet choose to "go on sinning" instead. In that case, they lack every possible excuse for their unbelief and will suffer all the more for it (John 9:41).