What did the 'service of God' involve in the Old Testament?
The service of God involved the tabernacle given to Moses, the Aaronic priesthood, and how priests operated, how the tabernacle and later temple were set up, how sacrifices were offered, and the feast days throughout Israel's religious calendar year. It belonged to the law system and pictured the coming Redeemer and salvation plan.
Les explains that Romans 9:4 lists "the service of God" among Israel's privileges. This service began when God gave the tabernacle to Moses and then set up the priesthood with Aaron as the high priest. It was part and parcel of the system of law, not just the Ten Commandments; the big picture of law included everything pertaining to worship and sacrifices. The services showed how the priests operated, how the tabernacle was set up, how later the temple was set up, how sacrifices were offered, and how the feast days were set up throughout their religious calendar year. Les emphasizes that this was not just empty religion with nothing behind it, but all the practice of the law that Israel enjoyed was a picture of the coming Redeemer and the plan of salvation believers experience today.
Who are Israelites; to whom pertaineth the adoption, and the glory, and the covenants, and the giving of the law, and the service of God, and the promises;