Hebrews 4:7

Again he limiteth a certain day
Since the seventh day of the creation was a day of rest which God entered into, and not man; and since the land of Canaan was a typical rest, which the unbelieving Israelites did not enter into, because of unbelief; and yet there must be persons, and there must be a time for them to enter into the true rest which God has left a promise of; therefore he has limited, fixed, and appointed a certain day, the Gospel dispensation, for believers to enter into it:

saying in David;
or by David, who was the penman of the 95th psalm, as may be learned from hence; and this is agreeably to, and confirms a rule which the Jews give, that those psalms which are without a title were written by David ^F7; the Spirit of God spake in him and by him, and plainly pointed out another day of rest from the above mentioned:

today, after so long a time;
as two thousand five hundred years from the first seventh day to the time of Moses, and five hundred years from the times of Moses and Joshua, to his:

as it is said;
the Alexandrian copy reads, "as it is before said", or, "above said", as the Vulgate Latin, and Syriac versions; that is, in ( Psalms 95:7 Psalms 95:8 ) before cited, ( Hebrews 3:7 Hebrews 3:8 )

today if you will hear his voice, harden not your hearts;
(See Gill on Hebrews 3:7), (See Gill on Hebrews 3:8).