Zachariah and his wife were very righteous people, so after years endears of serving the Lord, they couldn't understand they were left with no heir in their old age, but soon, very soon they would understand.
Zachariah was chosen to go burn incense for God, which was all normal, until an angel came to stand before, which was a pleasant, and extremely horryfing surprise. He came bearing even more pleasant and slightly scary news, he would soon have a child.
The angel told Zachariah the great news, and in true Bible fashion, Zachariah questioned it, saying him and his wife were very old and it was very unlikely for them to have a child. The angel then became angry and told Zachariah that because of this he would not be able to speak till the child was born.
Soon after this encounter it was known that Zachariah's was now pregnant, and everybody talked about, as they were all happy for the couple as they they had worked so much to have children, and during all this celebration, Zachariah said nothing.
Then Zachariah, trying to confirm his wife's wishes were his own as well, writes down his thoughts, clear for all to see "His name is John" but the second he does, his voice comes back to him, allowing him to speak once more.