The opening prayer also known as the invocation, establishes the tone of a religious ceremony.
Merriam-Webster Online Dictionaryinvocation (noun)
a) the act or process of petitioning for help or support , specifically often capitalized a prayer of entreaty (as at the beginning of a service of worship)
b) a calling upon for authority or justification
a formula for conjuring - incantation
an act of legal or moral implementation - enforcement