en_tn/1ki/08/31.md

is required to swear

This can be stated in active form. AT: "someone requires him to swear" (See: rc://en/ta/man/translate/figs-activepassive)

upon his own head

Here "head" refers to the whole person. AT: "on him" (See: rc://en/ta/man/translate/figs-synecdoche)

give to him according to his righteousness

"to give him what he deserves because he is righteous"