The First Amendment to the Constitution of the United States
"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."
This makes it sound like the government has decided not to create a forced, national religion - as was done in Europe (where our forebears came from) - and from which they wanted to depart - so they could live in a place where they would have the choice to do things differently if they chose. This Amendment makes it sound that the citizens of that new, free land may exercise their new right to exercise any religion or no religion as they choose.
What I see happening in the united states is that people believe that the government doesn't like religion and doesn't want it in any government-related, government-sponsored, or government-funded venue such as public schools or libraries. Furthermore, I think people believe that the government has stated that the practice of religion in public, or government-funded places, is unlawful.
It would be exceeding its mandate to include separating religion and state to mean that the government should actively hunt down, ferret out, or squash religion wherever it finds it. There is nothing about the government hating religion and not wanting it in their public schools or public places in this Amendment. It sounds more like the government is choosing to stay silent on the subject - uninvolved. This allows the individual the freedom to practice their religion or not. The government is specifically guaranteeing that right to its citizenry.
Since the government's official position in the very first Amendment of our Constitution, on having a religious-focused program (at a public school for instance), would be not to have an opinion on it, (and certainly not to prohibit a program based on religious reasons), it would be lawful for the citizenry to hold a religious program at a public library or a public school, and it would also be lawful for that citizenry to be able to attend or not attend as they choose - not as the government chooses... (as long as the concert was unremunerated by the government).
If the government's position is not to get involved with religion in any way, then government-funding of a concert at a government location would be "getting involved," and therefore be unconstitutional for the government - (they would be breaking their own law). (If the religious program at a government location was uncompensated by the government, it might be a different story.)