Why did Israel have all those sacrifices and feast days in the law?
The sacrifices and feast days were part of Israel's service of God under the broader system of law, not empty religion. They were indicative, picturing and looking forward to the coming Redeemer and the plan of salvation as experienced today.
Les explains that Paul lists the Israelites as those to whom pertain the adoption, glory, covenants, giving of the law, service of God, and promises. The service of God began when God gave the tabernacle to Moses and set up the priesthood with Aaron as high priest. These services were part and parcel of the system of law. People normally think of the law as the Ten Commandments, but the big picture of law included everything pertaining to worship and sacrifices. The services showed how the priests operated, how the tabernacle and later the temple were set up, how sacrifices were offered, and the setting up of all the feast days throughout their religious calendar year. Les teaches that all of this was indicative and looked forward to our own plan of salvation. It was not just a bunch of religion with nothing behind it; the practice of the law that Israel enjoyed was a picture of the coming Redeemer and the plan of salvation as we experience it 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;