John Calvin on Deuteronomy 28:19-20

19. Cursed shalt thou be when thou comest in. God here pronounces that all their undertakings should meet with ill success; for going out and coming in signifies their various actions, and the whole course of their life; and this is more clearly expressed in the next verse, where He denounces against them misfortune in all their affairs, in that God would confound and mar whatever they should undertake. The words מהומה, “Vexation.” — A V. “Bruising, trampling, destruction.” — Robertson, Clavis Pentateuchi.

מגערת, “Rebuke.” — A V. “Reproach,” from גער. — W מהומה, mehumah, and מגערת, migegnereth, are indeed variously explained. Still the sum comes to this, that God would be against them, so as to discomfit and overthrow all their counsels and labors. Hence we are taught that all men’s endeavors are useless and vain, unless they seek for success from God.