Jesus told his followers, "You are the ___ of the earth."

Answer: Salt

Jesus said, "You are the salt of the earth," warning that salt which loses its savor is good for nothing.

“You are the salt of the earth. But if the salt loses its savor, how can it be made salty again? It is no longer good for anything, except to be thrown out and trampled by men.”— Matthew 5:13 (BSB)