Matthew Poole and continuators on Luke 1:9

9 According to the custom of the priests office, his lot was to burn incense when he went into the temple of the Lord.

The Priests were Multiplyed to an exceeding Number, we find an account of more then 4000 upon the return out of the Captivity of Babylon, Ezra 3.36, 37, 38, 39. they were doubtless afterward multiplyed to a far greater number, Iosephus tells us there were a thousand in a Course; whether they held to twenty four Courses as in Davids time or no I cannot tell. There were several parts of the Priestly Office, which it seemeth by this Text, the Priests of the Course that Ministred, divided amongst themselves by a Lot, one part of their Work was to Burn Incense Morning and Evening. It seems this was that part of the Priestly Office, which Zacharias was by Lot to Exercise.

Marginal references: Exod. 30.7. Lev. 16.17.