Why send a goat off into the desert?

Leviticus 16:20-22. A sacrifice was a substitute, symbolically bearing sin and receiving its consequences. This goat, however, was a living sacrifice–banished from camp as a symbol of guilt removed far from the people and God’s presence. The people watched as the goat was led to a distant spot–a striking portrayal of God’s promise to remove their sins from them.

–The Quest Study Bible