Why have mercy with Israel?

Comfort, yes, comfort My people!" Says your God. "Speak comfort to Jerusalem, and cry out to her, That her warfare is ended, That her iniquity is pardoned; For she has received from the LORD's hand Double for all her sins." (Isaiah 40: 1-2) Thus says your Lord, The LORD and your God, Who pleads the cause of His people: "See, I have taken out of your hand The cup of trembling, The dregs of the cup of My fury; You shall no longer drink it. But I will put it into the hand of those who afflict you, Who have said to you, "Lie down, that we may walk over you.' And you have laid your body like the ground, And as the street, for those who walk over."(Isaiah 51: 22, 23)