Hebrews 4:5

And in this place again - In the ninety-fifth Psalm, already quoted, Psalm 95:3. This was a second rest which the Lord promised to the believing, obedient seed of Abraham; and as it was spoken of in the days of David, when the Jews actually possessed this long promised Canaan, therefore it is evident that that was not the rest which God intended, as the next verse shows.

And in this place again - Psalm 95:11.

If they shall enter - That is, they shall not enter; see the notes at Hebrews 3:11. The object of quoting this here seems to be two-fold:

(1) To show that even in this Psalm God spoke of "his" rest, and said that they should not enter into it; and,

(2) it is connected with Hebrews 4:6, and is designed to show that it was implied that a rest yet remained. "That which deserves to be called "the divine rest" is spoken of in the Scriptures, and as "they" did not enter into it, it follows that it must be in reserve for some others, and that the promise must still remain."

4:5 In this psalm, of a rest yet to come.