Isaiah 66:24

"Before they call, I will answer and while they are still speaking, I will hear."

God's response to Israel's plea for mercy comes in three parts:
1) Why Israel should not expect Mercy.
God lays out how time and again, Israel spurned relationship with God. He calls, they refuse to answer. They go whoring after other gods and polite His dwelling place with sin. God will judge, He will repay, and Israel deserves His wrath.
2) Portions
But, God divides this retribution into two groups: those who sought and those who forsook. Those who sought, are God's chosen, the remnant of believers. Those who forsook are the ones who will be destroyed. They refused the call to salvation and refused to listen to God, so now God refuses their cry for mercy and gives to them what they deserve.
3) Inheritance
But to the chosen, through no merit of their own, simply that God chose them for salvation and they believed, God gives an inheritance. It is filled with Joy (v.18-19 ) Life (v.20) Prosperity (v.21) Possession (v.22) Peace (v.23) and relationship with God.

God answers cries for mercy with the Gospel. "You do not deserve my mercy because of your sin. But because I have called you and because you are mine, I will not deal with you as your sins deserve, instead, I will pour out on you abundant blessing and give you an inheritance that befits my Son and I will form such a deep relationship with you that I will answer before you even know what to ask."
What Mercy!