Why did he request not to be brought in Mishpat?
Radak: Now (in the cave) I am in great affliction. If I sinned against You, do not punish me now, for You know that I am Avdecha!
Malbim: One who requests, he could be stood in Mishpat to weigh his deeds, whether or not based on Din, he is worthy that it be fulfilled. Such a Mishpat must consider a created being's liability to his Creator; refer to 143:2:2:2.
Why did he say "Ki Lo Yitzdak Lefanecha Kol Chai"?
Radak: If You look at all his deeds, no one is justified in front of You - how will I be justified in front of You?!
Malbim: If Hashem will come in Mishpat - considering His grandeur and the great good that He did for the supplicant - no one is justified in front of Him! His grandeur and benefits are unlimited - also His Avodah should be so, and creations, who are limited, cannot do so.
