Jamieson, Fausset and Brown on Jeremiah 44:25

25. Ye ... have both spoken with ... mouths, and fulfilled with ... hand--ironical praise. They had pleaded their obligation to fulfil their vows, in excuse for their idolatry. He answers, no one can accuse you of unsteadiness as to your idolatrous vows; but steadfastness towards God ought to have prevented you from making, or, when made, from keeping such vows.

ye will surely accomplish ... vows--Jeremiah hereby gives them up to their own fatal obstinacy.