What is the wisdom behind commanding Mary to fast from speech, with her saying to her people: "Indeed, I have vowed to the Most Merciful a fast, so I will not speak today to any human being"?

Mary was commanded not to speak, so that she might point to Jesus (peace be upon him), and he would speak, clarifying her innocence. Scholars have differed on whether she was commanded to say, "Indeed, I have vowed to the Most Merciful abstention [from speech], so I will not speak today to [any] human being," by tongue or by sign. The majority opinion is that it was by utterance, while Ibn Kathir favored the sign, and Al-Shanqeeti preferred that the sign take the place of speech. There is no contradiction between two matters: informing of a vow of silence, then adhering to it.