As per the 1st Amendment the government may neither endorse nor slander any sort of religious view. Doing this undermines the freedom and marginalizes those against the popular religion. In order to respect the separation between religion and state, we must remove:
1) "In God we Trust" from the dollar bill
2) "Under God" from the Pledge
3) Christian imagery (such as Nativity scenes) from PUBLIC property unless we also allow the imagery of atheists, Muslims, Hindus, Jews, etc. on the same plot of land.
The first and second points are clearly indicating that our government believes in a monotheistic God, this endorses religious views and marginalizes atheists and Hindus (to name two).
The third violates freedom of speech because without it we only allow Christians to express their views.