What is the comparison to "Sha'ar b'Nafsho"?
Rashi: Sha'ar has a Kamatz under the Shin and a Patach under the Ayin, and the accent is on the last syllable; it is a verb. If it were a noun, both vowels would be Patach, and the accent would be on the penultimate syllable, like every Sha'ar in Tanach. It is as if this eater spilled bile in the Nefesh of the stingy person. Sha'ar is like "ka'Te'enim ha'Sho'arim" (Yirmeyah 29:17); they are bitter.
R. Yonah: "Kemo" is Ka'asher (when), like "u'Chemo ha'Shachar Alah" (Bereishis 19:15). Sha'ar is like "Me'ah She'arim" (ibid. 26:12); it is estimation and quantity. When he estimated and assessed in his Nefesh...
Malbim: Scientists say that evil sparks come out of stinginess. Their root is in the lowliness of the Nefesh that looks with its stingy eye. They are like lethal sparks on the matter at which he looks. It was reported that a stingy person stared at bread, and death and bereavement were found in it.
Why does it say "Ken Hu"?
R. Yonah: When he estimated your nature and Midos like his, then he tells you 'eat and drink'...
Malbim: Sha'ar is a blemished, despised matter in his internal Nefesh; so is his bread.
What is the meaning of "v'Libo Bal Imach"?
R. Yonah: He hopes that you will not accept his words, and not listen to him. He says in his heart that you are stingy, like him, and you normally tell people to eat and drink, and you do not want them to. He thinks that also you will assess him like yourself, and know that he does not want you to eat. He relies on and hopes for this.
Malbim: He tells you 'eat and drink.' It seems to you that he did not put Ayin ha'Ra in it; However, his heart is not with you. Eating it will damage you to the point that you will vomit what you ate.
Malbim (according to the metaphor): Learning Chachmah is compared to consuming bread and water, like I explained regarding "Hoy Kol Tzamei Lechu la'Mayim" (refer to Yeshayah 55:1:3:3). One should not learn from a stingy person, for his heart is full of evil images and plans of sin, and so is his bread. He tells you to eat - it seems that he teaches to you Divrei Chachmah - his heart - the power that rules - is not with you. He does not rule over his Ru'ach to subdue his desires. Also the bread that you ate and the Chachmah that you already received, you will vomit it out, and you will ruin your nice ways.
