Why does it say "va'Yishach" and "va'Yishpal"?
Radak: Past tense used in place of future; this is common in Nevu'ah. A time will come when people will be lowly, and not be exalted due to much silver and gold and horses. This will be in the days of Mashi'ach, when all nations will gather to fight against Yerushalayim, and they will see that their silver and gold, strength and multitudes did not help them. Then their pride will be lowered.
Malbim: "Va'Yishach" means that his heart, Ru'ach and mind will be humbled. "Va'Yishpal" is via actions, e.g. fasting.
Why does it say "Adam" and "Ish"?
Rashi, Targum Yonasan: "Adam" is a small person. "Ish" is a great, valiant person. Radak (5:15) this is like "Gam Bnei Adam Gam Bnei Ish" (Tehilim 49:3)
Radak: The matter is repeated in different words.
Why did he say "Al Tisa Lahem"?
Rashi: The Navi tells Hashem, I know that You will not pardon them from exacting payment (punishment) from them.
Radak: Do not pardon what they did to Yisrael. Rather, punish them at that time for all that they did.
