7 God again set a certain day, calling it “Today.” This he did when a long time later he spoke through David, as in the passage already quoted: “Today, if you hear his voice, do not harden your hearts.”a

Read Hebrews 4:7 Using Other Translations

Again, he limiteth a certain day, saying in David, To day, after so long a time; as it is said, To day if ye will hear his voice, harden not your hearts.
again he appoints a certain day, "Today," saying through David so long afterward, in the words already quoted, "Today, if you hear his voice, do not harden your hearts."
So God set another time for entering his rest, and that time is today. God announced this through David much later in the words already quoted: “Today when you hear his voice, don’t harden your hearts.”