And there appeared unto him an angel of the Lord standing on the right side of the altar of incense.
All Commentaries on Luke 1:11 Go To Luke 1
Theophylact of Ochrid
AD 1107
It is said the altar of incense, because the other altar was set apart for burnt offerings.
As if when Zacharias asks, How shall I know this? the angel answers, Because Elisabeth shall bring forth a son, you shall believe that the sins of your people are forgiven.