Malbim: I should not be poor in Da'as, that I will not understand anything, to the point that I will come to believe in Shav - things with no substance at all, like idolaters, who believed in all follies.

Rashi: It is poverty.

Malbim: It is poverty of intellect.

Malbim: It is wealth of Sechel, to investigate too much, lest he conclude false matters, like many investigators said lies to deny creation of the world from nothing. They said that the world always existed, just like Hashem always existed, and perforce it came from Him, like a shadow from the sun, and an intellectual with ideas. They concocted lies in all facets of Emunah. One with too little intellect, or too much, is prone to depart from Emunah.

Rashi: It is an expression of food. The same applies to "Teref Nasan li'Yre'av" (Tehilim 111:5).

Malbim (the Nimshal): I should become wise via Chachmah of the Torah - the food of the Nefesh special for its perfection and health.