Rights before duties. Logically, freedom of religion should mean that the invited clergyman is free to pray after the manner of his own faith, not after the sanitized wordings that represent no specific religion. Otherwise, prayer cannot be honest or authentic. The conflict between revelation and politics is whether politics will allow revelation to state what it is, what it holds. The state wants to censor prayers lest they be unsettling to legislators, themselves defining good and evil.
Religion has a political restriction.
In this regard, the case of the Reverend Joseph Wright of Wichita is instructive. Wright is an Evangelical minister who was asked by his local legislator, a parishioner, to deliver the invocation before the Kansas legislature. This honor is a feature of American legislatures, including the federal legislature. Generally there are certain restrictions, about which the minister or priest or rabbi is informed before he can present himself. The Reverend Wright wrote his prayer in about a half-hour to give the following day before the Kansas Assembly.