Angel Gabriel

Who is “Gabriel” (Luke 1:19)?
Gabriel is one of the three angels named in the Bible; the other two are Lucifer, who rebelled against God, was hurled out of heaven, and became Satan, and Michael. Since Gabriel is positioned “before God” (Luke 1:19) instead of far away from Him, and “standing” (Luke 1:19) instead of prostrate, he is an archangel, as Michael also still is, and as Lucifer once was. Since Daniel chapters 8 and 9 mention Gabriel appearing to the Old Testament prophet Daniel, Zacharias immediately would have recognized his name.

Why was Zacharias made “mute” (Luke 1:20)?
Not only would Zacharias and his wife Elizabeth have a child as they had been praying for for decades, but their child will be the prophet like Elijah whom God had promised to send as His forerunner. And the arrival of the forerunner meant the imminent arrival of the Messiah. Upon hearing “these good news” (Luke 1:19), any Jew, let alone the priest of Israel chosen to burn incense on behalf of the nation, should have expressed joy, not doubt. The miracle of being made “mute and not able to speak until the day these things take place” (Luke 1:20) will help Zacharias believe, and since listening promotes learning more than speaking does, may also teach him to think before speaking the next time.

What “signs” (Luke 1:22) was Zacharias making to the people waiting outside the temple's sanctuary?
The sign language wasn't invented until 1817, so it must have become a spontaneous game of charades. There is no indication that anyone understood what Zacharias must have motioned with excitement and frustration.