a great millstone should be hung about his neck, and that he should be sunk into the depths of the sea

This can be stated in active form. AT: "if someone put a great millstone around his neck and threw him into the deep sea" (See: rc://en/ta/man/translate/figs-activepassive)

millstone

This is a large, heavy, circular stone used for grinding wheat grain into flour. AT: "a heavy stone"