'Hereby' in the Bible

Moses said, "Hereby you shall know that Yahweh has sent me to do all these works; for [I have] not [done them] of my own mind.

Joshua said, "Hereby you shall know that the living God is among you, and that he will without fail drive the Canaanite, and the Hittite, and the Hivite, and the Perizzite, and the Girgashite, and the Amorite, and the Jebusite out from before you.