Albert Barnes Commentary Hebrews 4:8

"For if Joshua had given them rest, he would not have spoken afterward of another day." — Hebrews 4:8 (ASV)

For if Jesus — a marginal note says, "That is, Joshua." The Syriac renders it, "Joshua the Son of Nun." Jesus is the Greek way of writing Joshua, and there can be no doubt that Joshua is intended here.

The objective is to prove that Joshua did not give the people of God such a rest as to make it improper to speak of a "rest" after that time. "If Joshua had given them a complete and final rest—if, by leading them to the promised land, all that the promise contemplated had been done—then it would not have been mentioned again, as it was in David's time."

Joshua did give them a rest in the promised land, but it was not all that was intended, and it did not exclude the promise of another and more important rest.

Then would he not — then God would not have spoken of another time when that rest could be obtained. The "other day" referred to here is the one previously mentioned by the phrase "today," and it refers to the time in which it is spoken of long after Joshua, namely, in the time of David.