Hebrews 4:6

it remaineth--still to be realized. some must enter--The denial of entrance to unbelievers is a virtual promise of entrance to those that believe. God wishes not His rest to be empty, but furnished with guests (Luk 14:23). they to whom it was first preached entered not--literally, "they who first (in the time of Moses) had the Gospel preached to them," namely, in type, see on Heb 4:2. unbelief--Greek, rather "disobedience" (see on Heb 3:18).

The apostle, having in the foregoing chapter set forth the sin and punishment of the ancient Jews, proceeds in this, I. To declare that our privileges by Christ under the gospel exceed the privileges of the Jewish church under Moses, as a reason why we should make a right improvement of them (Heb 4:1-4). II. He assigns the cause why the ancient Hebrews did not profit by their religious privileges (Heb 4:2). Then, II. Confirms the privileges of those who believe, and the misery of those who continue in unbelief (Heb 4:3-10). IV. Concludes with proper and powerful arguments and motives to faith and obedience.

4:6 So God’s rest is there: Building on the discussion in 4:3-5, the author is about to argue that the promised rest is still available (4:7-10). But those who wandered in the wilderness, even though they heard the good news that the Promised Land was open to them, failed to enter because they disobeyed God (see Num 14:1-25; Deut 1:19-46; Ps 106).