Charles Spurgeon Commentary Hebrews 4:6-8

"Seeing therefore it remaineth that some should enter thereinto, and they to whom the good tidings were before preached failed to enter in because of disobedience, he again defineth a certain day, To-day, saying in David so long a time afterward (even as hath been said before), To-day if ye shall hear his voice, Harden not your hearts. For if Joshua had given them rest, he would not have spoken afterward of another day." — Hebrews 4:6-8 (ASV)

We read of this in Psalm 95, where David was urging those to whom he was writing to hear God's voice, and not be like the unbelievers in the wilderness, so that the rest still remained to be entered upon by someone. Joshua had not given them rest, or else David would not have spoken of entering into rest.