John Gill Commentary Luke 1:8

"Now it came to pass, while he executed the priest`s office before God in the order of his course," — Luke 1:8 (ASV)

And it came to pass, that while he executed the priest's
office
To which he was called and ordained, even to offer gifts and sacrifices for men; whilst he was in the way of his duty, when oftentimes God appears to, and in favour of his people; whilst he was performing it,

before God ;
in the temple, where was the symbol of the divine presence, before the altar of the Lord; and as having the fear of God before his eyes; considering himself as in the sight of God, and doing his work faithfully and sincerely:

in the order of his course ;
taking his turn in the order of the course of Abia, to which he belonged; (See Gill on Luke 1:5).