Matthew Poole and continuators on Hebrews 4:6

6 Seeing therefore it remaineth that some must enter therein , and they to whom it was first preached, entred not in because of unbelief .

The Spirit having demonstrated, that God's Rest sworn to Believers in the Gospel, and mentioned by David, could not be the seventh Days Rest; proceeds to prove likewise, that it could not be the Rest of Israel in the Land of Canaan, since that was entred into 400 years before he wrote by the Spirit of this better Rest, since those unbelieving Israel that entred into Canaan never entred into this Rest. Forasmuch then as a Rest to come is spoken of, and that some Believers must have a real and full possession of the glorious Rest offered to them in the Gospel, as David foretold; see v. 9.10, 11.

The unbelieving Israel who had the glad Tidings of this Rest preached unto them by Moses and by David, &c. yet entred not into it, tho they entred into, and lived in Canaan, because of their Disobedience and Unbelief. Then it follows Canaan's Rest and this cannot be all one; and the latter is only intended by David here.

Marginal references: Or, the Gospel was first preached.