World Wide Study Bible
a Bible passage
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 (Lu 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).