Hebrews 3:15

“for he is our God and we are the people of his pasture, the flock under his care. Today, if only you would hear his voice, do not harden your hearts as you did at Meribah, as you did that day at Massah in the wilderness,”

The author of Hebrews quotes Psalm 95:7-8 in Hebrews 3:7-8, and refers to it again here.

“But encourage one another daily, as long as it is called “Today,” so that none of you may be hardened by sin’s deceitfulness.”

Shares the theme of heeding God's voice and avoiding a hardened heart.

“Therefore God again set a certain day, calling it “Today,” 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.””

Repeats the 'Today' exhortation from Psalm 95, emphasizing the urgency of obedience.

“For he says, “In the time of my favor I heard you, and in the day of salvation I helped you.” I tell you, now is the time of God’s favor, now is the day of salvation.”

Shares the sense of urgency to respond to God's call 'today'.

“Whoever remains stiff-necked after many rebukes will suddenly be destroyed—without remedy.”

Connects to the warning against hardening one's heart.