C. F. Keil and Franz Delitzsch on Proverbs 28:27

Pro 28:27 27 He that giveth to the poor suffereth no want;      But he that covereth his eyes meeteth many curses.

In the first line the pronoun לּו, referring back to the subject noun, is to be supplied, as at Pro 27:7 להּ. He who gives to the poor has no want (מחסּור), for God’s blessing reimburses him richly for what he bestows. He, on the other hand, who veils (מעלּים( sl, cf. the Hithpa., Isa 58:7) his eyes so as not to see the misery which calls forth compassion, or as if he did not see the misery which has a claim on his compassion; he is (becomes) rich in curses, i.e., is laden with the curses of those whose wants he cared not for; curses which, because they are deserved, change by virtue of a divine requital (vid., Sir. 4:5f.; Tob. 4:7) into all kinds of misfortunes (opp. רב־בּרכות, 20a). מארה is constructed after the form מגרה, מקרה from ארר.