Overall meaning : As for those who accuse their wives of adultery but have no witnesses to prove such accusation except themselves, the husband must, in order to discharge himself from the imputation and penalty of slander, swear four times by Allah that he is telling the truth, and in a fifth time calls down upon himself the curse of Allah if he is lying. To free herself from the imputation and penalty of adultery (which is stoning to death), the wife must swear four times by Allah that her husband’s charge is false, and in a fifth time calls down Allah’s curse upon herself if her husband is telling the truth.
Had it not for Allah’s favour and grace towards you and the fact that He showed mercy to those of you who repented and turned to Him and that He is wise and His laws are judicious (including the law of mutual cursing demonstrated here), He would have hastened to punish you for such sin.