Why does it say "Erech Apayim Rav Tevunah"?
R. Yonah: One who rules over his anger, and does not take vengeance at the time of his anger until his mind is settled, and he thinks properly what to do, from this Midah he will come to be Rav Tevunah. His heart investigates if there is reason to refute his initial idea. Via Erech Apayim, he purifies his heart from getting angry over worldly follies, and turns to seek Chachmah.
Malbim: A law of Tevunah is to delay anger and not immediately avenge.
What is "Merim Iveles"?
Rashi: He separates it for his portion.
Malbim: Refer to 14:29:3:2-3.
Why does it say "u'Ketzar Ru'ach Merim Iveles"?
R. Yonah: A Ketzar Ru'ach will never reach investigation, for he adopts the first idea that is good to him. His heart does not want to investigate if there is reason to refute his idea. Also, when he hears something that his Da'as does not accept initially, he cannot investigate it. He immediately rejects it. A Ba'al Tevunah hearkens, investigates, and sometimes accepts it in the end. Also, anger and Ketzar Ru'ach befuddle thinking, and he cannot investigate properly. If a Chacham gets angry, his Chachmah departs (Pesachim 66b). When one is angry, his lips immediately reveal all that crosses his Ru'ach, e.g. pride and disgrace. As long as he holds back his lips from revealing this, he lowers and subdues bad natures and hated thoughts - "v'Im Zamosa Yad l'Feh" (30:32), "Zamosi Bal Ya'avar Pi" (Tehilim 17:3). When he verbalizes and makes known his heart's intents, he strengthens the folly in his heart, and strengthens its root in his nature. 1
Malbim: One can be Erech Apayim but Ketzar Ru'ach - his heart is not serene, and his Ru'ach immediately brings up images of vengeance; this is Iveles against the laws of Chachmah. He raises Iveles from the depths of the Nefesh to outside.
Malbim (30): One who puts images of envy, that he is zealous for his honor on his heart, this opposes Chachmah and he destroys himself, for the heart heals life of the flesh. If one's strength weakens, his life and cure depend on the heart. When the heart is strong, it sends its springs (blood) through the arteries. They give to the body to drink, and revive it. Putting images of envy on his heart consumes the flesh and makes the bones rot, and his body is finished off - "mi'Kol Mishmar Netzor Libecha Ki Mimenu Totz'os Chayim" (4:23).
R. Yonah: Troubles constantly occur that anger people; the world is mostly sad. Therefore, one must uproot love of the world from his heart, lest its sadness cloud him, and its rejoicing should not increase his Simchah. One of these cannot be without the other. When he uproots them, his heart will be clean to investigate Chachmah.
