The people of God who supposed to serve God  ...

Although God told Moses whom He called at Mount Sinai that after delivering the Israelites from Egypt,

they should worship God at Mount Sinai (Exod. 3:1-12),

they made a molten calf and worshiped it when Moses was on Mount Sinai (32:4).

Just as the people of God who supposed to serve God actually served the fertility bull in the land of Goshen Egypt

as a fertility and abundance god (internet), they made the molten calf and worshiped it under Mount Sinai.