The phrase "the border" refers to the border of Egypt. AT: "a stone pillar to Yahweh at the border of Egypt" (See: [[rc://en/ta/man/translate/figs-explicit]])
The abstract nouns "sign" and "witness" can be expressed with the verbs "show" and prove." AT: "The altar will show and prove that Yahweh of hosts is in the land of Egypt" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])
Yahweh being in the land of Egypt represents the people of Egypt worshiping him. AT: "that the people in the land of Egypt worship Yahweh of hosts" (See: [[rc://en/ta/man/translate/figs-explicit]])
Who Yahweh will deliver them from can be made explicit. AT: "Yahweh will deliver the Egyptians from their oppressors" (See: [[rc://en/ta/man/translate/figs-explicit]])