Proverbs 28:27 He that giveth unto the poor shall not lack: but he that hideth his eyes shall have many a curse.
The conditional promise is: if you give to the poor, then you will not lack. The condition is clear: give to the poor; that’s easy to understand. The antithetical parallel, “hide your eyes,” then means to avert your gaze, avoid, ignore and pass by the poor man, the beggar, the homeless.
The promise, “you will not lack,” admits of several explanations: 1) It can mean not lack anything at all, as in “the Lord is my shepherd, I shall not want” for anything. But that is an unconditional promise independent of whether we give to the poor or not; 2) it can mean to simply not lack anything spiritually, as in “my God will supply every need of yours according to his riches in glory.” But that is also an unconditional promise; 3) The context here seems to mean not lack any tangible, physical, earthly money as in “give and it shall be given you.” God gives to the poor through a conduit, you, and when He sees you give He gives you more so you can give more. “God gives to the giver.”
The opposite threat and warning to the unbeliever who refuses to give is that he will “have many a curse.” These then would be earthly curses; monetary goods will be devoured by accident, injury, illness, unforeseen expenses, etc.
This promise is given to us so that the Lord may encourage us to be generous, kind, and giving. You will not miss it; you will have enough; you will not lack. Trust the Lord to provide.