Must I enter into a new marriage contract after I told my wife, with whom I have not consummated the marriage, "If you do not say such and such, you will be divorced," and then I took her back, believing it to be a single divorce, or can this be considered an oath (yamin) that necessitates an expiation for an oath (kaffarat yamin), and that suffices to rectify the marriage?

If your statement to your wife, "you will be divorced," was intended as a promise of divorce and not as a suspension (ta'liq) of divorce, then the divorce does not occur. However, if you intended to suspend the divorce on her disobedience, and the disobedience occurred, then the divorce takes place. It is permissible to act upon the fatwa of a trustworthy scholar, as long as it is not driven by caprice. If you acted upon the opinion of the majority regarding the occurrence of the divorce, scholars have differed on the permissibility of retracting this adherence (taqleed). Therefore, we advise presenting the matter to a Sharia court or to trustworthy people of knowledge.