The services in the Temple were conducted by twenty-four courses of priests, which had been first ordained about a thousand years before by David. The priests comprising each course had to go up to Jerusalem twice a year to minister. At the time of which we are speaking the course of Abia was serving.
We cannot stay to go into all the varied duties which the priests had to perform in the Temple, but of all those duties, that of the daily offering of incense was so honourable that no one was allowed to perform the duty twice. It was determined by lot who should offer, and the lot had fallen upon the aged priest Zacharias. He was a descendant of Aaron, and could boast a genealogy going back fifteen centuries. Elisabeth, his aged wife, was also of the priestly line, for she too was descended from Aaron. When the time came for Zacharias to fulfil his course of duty at the Temple he left his wife behind in the hill country of Judea. We can imagine how lonely she would be, for she had no son or daughter to bear her company, and cheer her with their companionship. This was a cause of sorrow to both Elisabeth and Zacharias.
Excerpt from The Life of Jesus Christ by W.R. Mitchell
Read what happens next in Luke 1:5-24.