And your strength shall be spent in vain. — That is, with the heaven over them as metal, their labour expended in ploughing, digging, and sowing will be perfectly useless.
Your land shall not yield her increase, as no amount of human labour will make up for the want of rain. In Deuteronomy 11:17, where the same punishment is threatened, and the same phrase is used, the Authorised Version unnecessarily obliterates the identity of the words in the original by rendering them “the land yield not her fruit.”