What did Yahweh tell Ezekiel to do with a brick?

Yahweh told Ezekiel to carve the city of Jerusalem on a brick and then lay seige against it [4:1; 4:3]

Why did Yahweh tell Ezekiel to do this with a brick?

Yahweh told Ezekiel to do this as a sign to the house of Israel [4:3]