Part of the Christmas Story is the sharp contrast in how Mary vs. Zacharias the priest responded when they were visited by the archangel Gabriel (Luke 1:1-20). Mary responded in faith.
But Zacharias responded in disbelief.
The angel replied to Zacharias (Luke 1:18-19),
The majority opinion is that Zacharias was punished for his unbelief. But I prefer the minority opinion. Proverbs 18:21 says,
In the minority view, Zacharias was silenced to ensure that the prophecy would be fulfilled. In this view, Zacharias had the potential to block John's miraculous birth by speaking negative words of unbelief over Gabriel's prophecy. Therefore, the power of speech was taken away from him until John was born. Words have power! God spoke the world into being by the power of His words. Humans are made in God’s image, and our words also have power - for better or worse, for good or evil, to allow prophecy to be fulfilled or to block it by unbelief. Regardless of why Zecharias was struck dumb, he probably believed the prophecy after Gabriel silenced his voice!
Heidi Baker of Iris Ministries says that when God gives you a promise, it can be like a (very long!) pregnancy. It may take years before you see the "birth" of your promise. I've been holding on to a promise for nearly 30 years! But if you give up and stop believing in God's promise, that is like aborting your unborn baby. Your promise from God can "die in the womb" because of your unbelief.