It's supposed to be kinda like King's Gambit where you give up a pawn to take their pawn out of the center, but the only problem is that if black play Qh5+, the only peice that can block is the pawn. White can also line up a battery with Be2 before the queen move and then the king would have to move. A similar idea is c5 after white plays d4.
This is called the Old Benoni defense and it is better because black's bishop and knight can block a check on that diagonal.
i personally