Seeing therefore it remaineth that some must enter therein - That is, "Since there is a rest spoken of in the Scriptures, implying that it is to be enjoyed by some, and since they to whom it was first promised did not inherit it, it follows that it must still be in reserve." This is the conclusion which the apostle draws from the argument in the previous verses, and is connected with Hebrews 4:9, where he says that "there remaineth a rest to the people of God" - the point to which the whole argument tended. The statement in Hebrews 4:7, Hebrews 4:8, is to be regarded as an "interruption" in stating the conclusion, or as the suggestion of a new thought or a new argument bearing on the subject, which he sets down even while stating the conclusion from his argument. It has the appearance of being "suggested" to him as a new thought of importance, and which he preferred to place even in the midst of the summing up of the argument rather than omit it altogether. It denotes a state of mind full of the subject, and where one idea came hastening after another, and which it was deemed important to notice, even though it should seem to be out of place. The "position" in this Hebrews 4:6 is, that it was a settled or indisputable matter that some would enter into rest. The implied argument to prove this is:
(1) that there was a "rest" spoken of which deserved to be called a "divine rest," or the "rest of God;"
(2) it could not be supposed that God would prepare such a rest in vain, for it would follow that if he had suited up a world of rest, he designed that it should be occupied. As he knew, therefore, that they to whom it was first offered would not enter in, it must be that he designed it for some others, and that it "remained" to be occupied by us now.
And they to whom it was first preached - Margin, "The Gospel." Greek "Evangelized;" that is, to where the good news of the rest was first announced - the Israelites. "Entered not in because of unbelief;" see the notes at Hebrews 3:19.

It remaineth that some must enter therein - Why our translators put in the word must here I cannot even conjecture. I hope it was not to serve a system, as some have since used it: "Some must go to heaven, for so is the doctrine of the decree; and there must be certain persons infallibly brought thither as a reward to Christ for his sufferings; and in this the will of man and free agency can have no part," etc, etc. Now, supposing that even all this was true, yet it does not exist either positively or by implication in the text. The words επει ουν απολειπεται τινας εισελθειν εις αυτην, literally translated, are as follows: Seeing then it remaineth for some to enter into it; or, Whereas therefore it remaineth that some enter into it, which is Dr. Owen's translation, and they to whom it was first preached (οἱ προτερον ευαγγελισθεντες, they to whom the promise was given; they who first received the good tidings; i.e., the Israelites, to whom was given the promise of entering into the rest of Canaan) did not enter in because of their unbelief; and the promise still continued to be repeated even in the days of David; therefore, some other rest must be intended.

Seeing therefore it remaineth,.... It follows by just consequence,
that some must enter therein; for God's swearing concerning some, that they should not enter into his rest, supposes that others should: and
they to whom it was first preached; to whom the Gospel was first preached, namely, the Israelites in the wilderness: entered not in because of unbelief; See Hebrews 3:19.

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 (Luke 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 Hebrews 4:2.
unbelief--Greek, rather "disobedience" (see on Hebrews 3:18).