In the beginning of his speech, how does patrick henry immediately establish ethos?

If you mean the speech to the Virginia Convention, then he builds ethos through religious passion. He portrays himself as a faithful Christian who is fighting for God. The allusion to the Biblical motif of light is the equivalent of fighting for God's truth. 

Britain and its empire stood alone against hitler and mussolini. in june 1941, hitler broke the non-aggression agreement with stalin and germany invaded the soviet union. in december, japan attacked the us and britain. the main lines of world war ii had formed.