To what two choices facing the colonists does patrick henry refer in his opening lines? how does he defend his need to speak about them?

The speech that the problem is pertaining to is the Second Virginia Convention. Patrick Henry sustained the colonists' rights to make their own laws and cry out, "If this be treason, make the most of it."  For ten years, he sustained to argue boldly for colonial rights.  He played a noticeable role in the Revolution and the citizens of Virginia designated him to be the first governor under its new constitution. He says that the colonists must choose between slavery and freedom. Because he is putting first the law of the Lord before man’s law. He does this with at least a little apprehension, for he is about to speak words and notions that could be measured as treasonous. He rather reprimands the members for not wanting to hear the complete truth, so the first thing he did is to encourage them and reasoning so they can make a better judgement. 

yup its an addiction