As an example, he pointed to a ruling in California that barred students from saying the Pledge of Allegiance with the phrase "one nation under God."
No one can STOP you from saying it.

That would be against Freedom of Speech.

But they cannot REQUIRE that you say it. In any way.

The Constitution says the government cannot "establish" or promote religion, but Scalia said the framers did not intend for God to be stripped from public life.
Nor has it been. Anyone can believe in any religion s/he wants to. Even attend churches dedicated to that religion. And so forth. No one has taken it out of "public life".

"That is contrary to our whole tradition, to 'in God we trust' on the coins, to (presidential) Thanksgiving proclamations, to (congressional) chaplains, to tax exemption for places of worship, which has always existed in America."
So it is a tradition now?