Luke 1:20

“And behold, thou shalt be dumb, &c. Or "silent; and not able to speak", if he would. Silence is sometimes voluntary; but this was what he could not help; until the day that these thing shall be performed; which he had said concerning the conception and birth of a son, and the imposition of a name on him; for this dumbness remained upon Zachariah, not only until his wife had conceived, and the child was born, but until the eighth day after, when he was circumcised, and his name was given him the angel directed to: "because thou believest not my words": he was struck both deaf and dumb, as appears from his friends making signs to him, Luk 1:62 which they had no need to have done, could he have heard: he was struck with deafness, because he hearkened not to the angel's words; and with dumbness, because from the unbelief of his heart he objected to them. We learn from hence, what an evil unbelief is, and how much resented by God, and how much it becomes us to take heed, that it prevails not in us: and especially since it easily besets us: "which shall be fulfilled in their season"; first the conception, then the birth; after that the calling him by his name, and in process of time, the doing of his work and office; so that the unbelief Zacharias did not make the faith of God of none effect; for though sometimes the people of God are very unbelieving, yet he abides faithful to his word and promises. Mahomet, in his Alkoran (k), very wrongly makes the angel to say these words to Zacharias, "thy sign shall be, that thou shalt speak unto no man for three days, otherwise than by gesture. And elsewhere (l) it is said three nights, (k) C. 3. p. 40. Ed. Sale. (l) C. 10. p. 249.”

“Thou shalt be dumb - Σιωπων silent; this translation is literal; the angel immediately explains it, thou shalt not be able to speak. Dumbness ordinarily proceeds from a natural imperfection or debility of the organs of speech; in this case there was no natural weakness or unfitness in those organs; but, for his rash and unbelieving speech, silence is imposed upon him by the Lord, and he shall not be able to break it, till the power that has silenced him gives him again the permission to speak! Let those who are intemperate in the use of their tongues behold here the severity and mercy of the Lord; nine months' silence for one intemperate speech! Many, by giving way to the language of unbelief, have lost the language of praise and thanksgiving for months, if not years!”

“On account of the many signs the angel had given, that what he said was true, the unbelief of Zacharias seemed inexcusable; for the angel appeared in a holy place, in the temple, and during divine service: he, moreover, foretold what related to the redemption of all the people, and to the glory of God; from all which circumstances, Zacharias ought to have concluded, that it was a good angel, and that what he said would eventually come to pass. (Nicholas of Lyra) — Shalt be dumb, &c. He seems to have been both dumb and deaf by the Greek text, and by what we may learn from ver. 62; where we find, that those who were present did not speak, but rather made signs to him. (Witham)”