1. The first amendment also deals with religion and the state. Supporters of Manifest Destiny used God as their justification. But Manifest Destiny was little more than secular imperialism with a different name--in other words, the state was imposing itself on religion. And yes, I'm sure that there were individual Quakers and Pietists who supported MD--just as there were those, whose religious organizations went along with MD, who objected that the policy was (1) the moral equivalent of robbery (count me in!) and (2)blasphemous because it assumed that God had presented a new revelation pertaining to the US.
2. If crystal balls were part of sanctioned law, this might be a valid point.
3. No, I'm saying that God was a non-citizen, non-elected official/non-member of the state department. There is nothing in the Constitution that would have granted him/her policy direction.