Charles Ellicott Commentary Luke 1:20

"And behold, thou shalt be silent and not able to speak, until the day that these things shall come to pass, because thou believedst not my words, which shall be fulfilled in their season." — Luke 1:20 (ASV)

Behold, thou shalt be dumb.—The question was answered, the demand for a sign granted, but the demand had implied a want of faith, and therefore the sign took the form of a penalty. The vision and the words of the angel, harmonizing as they did with all Zechariah’s previous convictions, ought to have been enough for him.