Why did he say "Im Yachalof v'Yasgir"?
Rashi: If He will switch and afflict [one whom he wants to afflict...]
Ibn Ezra: This is like "Kol Bnei Chalof" (people, who pass from the world).
Devar Eliyahu: The verse teaches about three judgments on man - Gilgul (reincarnation), Gehinom or Kaf ha'Kela, [being slung] to the place where he sinned. "Im Yachalof" is being switched [in another Gilgul]. Yasgir is in Gehinom - "Yisgor Al Ish v'Lo Yipase'ach" (12:14). "V'Yakhil" is gathering all the litigants to him.
Malbim: After the assumption that man cannot understand Elokus, he cannot understand His knowledge, which is Himself. It is unlike our knowledge. He can know all future details, yet man still has choice. These cannot co-exist regarding our knowledge. Hashem can make someone pass from the world, or incarcerate (afflict) him.
Whom will He gather?
Rashi: His entire entourage, to debate about the one whom He wants to afflict.
Malbim: He can gather the entire world to ask them if He judged him properly.
What is the meaning of "u'Mi Yeshivenu"?
Rashi: Who can answer Him, to censure His act? Even the defeated was serene for a long time, so is His way [to afflict one who used to serene].
Malbim: Who can tell him 'You already knew that he will sin, so he had no choice'?
