Why was the scapegoat presented alive before the Lord?
The scapegoat was presented alive before the Lord to make atonement, or a covering, with it, and then to be let go into the wilderness. It symbolically bore Israel's sins away, taking the blame for wrongs and sins as it was released into the unknown, untracked wilderness.
Les explains that with the two goats, lots were cast. One goat was the Lord's lot and was sacrificed as a sin offering. The other was the scapegoat, presented alive before the Lord to make an atonement or covering, and then let go into the wilderness. Les points out that this live goat symbolically had the sins of Israel placed on it and was taken alive into the unknown, untracked wilderness—an uninhabitable, God-forsaken place—carrying the blame away. He notes we still use the term scapegoat today for the one who takes the blame for someone else's wrongs and sins.