The emphasis in Hebrews is that true believers have an eternal salvation (future rest) because they trust a living Saviour who constantly intercedes for them. But the writer was careful to point out that this confidence is no excuse for sin. God disciplines His children.
Christians who doubt God’s Word and rebel against Him do not miss out on heaven, but they do miss out on the blessings (present rest) that God has in store for them just as God disciplined Israel in the wilderness for forty years.
Hebrews 4:1 ‘Therefore, since the promise of entering his rest still stands, let us be careful that none of you be found to have fallen short of it.’