Why should you not exert to get rich?
Rashi: Do not try to learn bundles and bundles [of teachings]; in the end, you will forget them.
R. Yonah: If you attain your necessary food with an intermediate amount of toil, do not exert and toil more than needed in order to get rich.
Mesilas Yesharim (Perek 21): Hishtadlus (efforts) do not help, just it is necessary. Once he did some, he fulfilled his obligation, and there is room for Shamayim's Brachah to dwell on him. He need not spend his days in diligent Hishtadlus.
Malbim: After commanding not to be drawn after desire for eating and pleasure, he commands not to be drawn after gathering wealth. Via this, one abandons contemplating Torah.
Why should you refrain from Binah?
R. Yonah: Wealth does not depend on diligence; it depends only on Hashem's decree. One can exert day and night and not get rich. Cease from your Binah if it seems to you according to your intellect that you will get rich, "v'El Binasecha Al Tisha'en" (3:5). Why consume your strength for a Safek?
Malbim: The verse means, if you exert to get rich, you will refrain from your Binah - not all who increase business get wise (Avos 2:5), "v'Lo me'Ever la'Yam Hi" (Devarim 30:13), like Chazal said (Torah is not found in merchants - Eruvin 55a).
