"Hashem is not a man, that he should repent." Should G-d repent? Is He a man?
If Hashem is not able to repent then why do we pray for mercy, why pray at all? If He is not able to repent then is He able to forgive or to have mercy or can He accept our repentance?
Jer 18:4-6 And the vessel that he made of clay was marred in the hand of the potter: so he made it again another vessel, as seemed good to the potter to make [it]. Then the word of the LORD came to me, saying, O house of Israel, cannot I do with you as this potter? saith the LORD. Behold, as the clay [is] in the potter's hand, so [are] ye in mine hand, O house of Israel.
He is able to give us a new start... to reshape our heart if we let Him. The L-rd is able to repent, but he is not obliged to us to repent. We are His workmanship and can not demand that He repent to us as we may demand to a man to repent. There are times where He has repented (to be sorry, be moved to pity, have compassion, suffer grief, repent) and times where He has not.
Consider these verses as well:
Gen 6:6 And it repented the LORD that he had made man on the earth, and it grieved him at his heart.
Exd 32:14 And the LORD repented of the evil which he thought to do unto his people.
2Sa 24:16 And when the angel stretched out his hand upon Jerusalem to destroy it, the LORD repented him of the evil, and said to the angel that destroyed the people, It is enough: stay now thine hand. And the angel of the LORD was by the threshingplace of Araunah the Jebusite.
1Ch 21:15 And God sent an angel unto Jerusalem to destroy it: and as he was destroying, the LORD beheld, and he repented him of the evil, and said to the angel that destroyed, It is enough, stay now thine hand. And the angel of the LORD stood by the threshingfloor of Ornan the Jebusite.
Jer 26:19 Did Hezekiah king of Judah and all Judah put him at all to death? did he not fear the LORD, and besought the LORD, and the LORD repented him of the evil which he had pronounced against them? Thus might we procure great evil against our souls.
Amo 7:3 The LORD repented for this: It shall not be, saith the LORD.
Amo 7:6 The LORD repented for this: This also shall not be, saith the Lord GOD.
Gen 6:6 And it repented the LORD that he had made man on the earth, and it grieved him at his heart.
Jdg 2:18 And when the LORD raised them up judges, then the LORD was with the judge, and delivered them out of the hand of their enemies all the days of the judge: for it repented the LORD because of their groanings by reason of them that oppressed them and vexed them.
Jer 20:16 And let that man be as the cities which the LORD overthrew, and repented not: and let him hear the cry in the morning, and the shouting at noontide;
Zec 8:14 For thus saith the LORD of hosts; As I thought to punish you, when your fathers provoked me to wrath, saith the LORD of hosts, and I repented not: