Question

there is no doubt, of course, that the crèche itself is capable of communicating a religious message.... thus, by permitting the display of the crèche in this particular physical setting,... the county sends an unmistakable message that it supports and promotes the christian praise to god that is the crèches religious message.... thus, by prohibiting government endorsement of religion, the establishment clause prohibits precisely what occurred here: the governments lending its support to the communication of a religious organizations religious message.
-justice harry blackmun,
opinion of the court,
county of allegheny v. aclu
1989
according to blackmuns decision, why did the crèche display violate the establishment clause?
it was located inside a county building.
it was not accompanied by a menorah.
it celebrated the origin of a religious holiday.
it forced county workers to honor a religious figure.

Explanation:

The text states that the crèche's religious message (Christian praise to God) was supported by the county (government) through its display. The Establishment Clause prohibits government endorsement of religion. The key is that the display was a government - supported communication of a religious organization's message related to the origin of a religious holiday (Christmas, as the crèche is associated with the Nativity, a Christian religious event).

Answer:

It celebrated the origin of a religious holiday.