It is often asked why Zacharias was punished for doubt (Luke 1:18), whereas Mary was not for asking what appears to be a similar question (Luke 1:34).

However, looking closely at what each person was actually asking reveals they are not exactly the same. Zachariah had been told outright that he would have a child, and as a priest, he knew God could do it and should not have questioned the promise.

Mary's inquiry, however, is not one of doubt of power, but one concerning the mechanism whereby the conception would occur. It had not been revealed to her until after this question that the conception would not require a human father. The two questions are of a different order, despite their similarity.