King James Bible
"And it came to pass, that while he executed the priest’s office before God in the order of his course,"
Zechariah was actively serving as a priest in the temple, performing sacred duties in God's presence. This emphasizes the holy setting where the upcoming angelic encounter will occur, highlighting that God often reveals himself during ordinary acts of faithful service. Priests served in rotating divisions established by King David (1 Chronicles 24), with each division serving twice yearly for one week. This detail underscores the organized, systematic nature of temple worship and places Zechariah's service within the long tradition of Israel's priesthood.