As Yahweh your God lives

This is an oath used to emphasize that what he is saying is true.

there is no nation or kingdom where my master has not sent men

Here "no nation or kingdom" is an exaggeration that means that men have traveled very far and gone to many places to find Elijah. This can be expressed positively. AT: "my master has sent men to nations and kingdoms near and far" (See: rc://en/ta/man/translate/figs-hyperbole and rc://en/ta/man/translate/figs-doublenegatives)