Luke 1:14 Zacharias was told that the birth of his son, John the Baptist would bring joy and gladness and that MANY would rejoice at his birth.
Luke 1:5-25, 39-45, 56-80, and Bible Dictionary: "John the Baptist"
What a blessing for Elisabeth and Zacharias to be able to have a son, after many years of barrenness. The family would of course rejoice at bringing a child into their family. As Mary came to Elisabeth and spoke with her about how they were both expecting and of how it all came about, their was much rejoicing as they found that Heavenly Father was blessing them and that they were instruments in the Lord's hands to bring about some very important things. After Mary left, Elisabeth bore John and both were healthy, which was something to rejoice as I am sure family was concerned for the health of Elisabeth as well as John. There were many miracles that came about that would help the family and the people see that there was something great to be had for this child, as they came to naming him John and at this point Zacharias was again able to speak.