1)
Why did he say "Mah Li va'Lach"?
1.
Malbim: A Navi's Tefilah helps only for those who believe in Hashem and His prophets. Then there is a connection between the Navi and the one he prays for.
2)
What is the meaning of "Al Ki Kara Hashem
1.
Rashi citing Targum Yonasan: Please 1 do not mention the sins of that evil man. Request mercy for us
1
Radak: Also Onkelos translated "Al Na Adon-ai" (Bereishis 19:18) as 'b'Va'u Che'an Ribonai.'