To “invoke” is to “call forth” and is traditionally associated with calling upon God. You can also think of it as invoking the spirit of your community—its vision of justice, its playful energy, or its familial feeling. Invocations can also serve to introduce the theme that you’ll be exploring in the service. (In Unitarian Universalist worship if there is an Invocation there are generally not Opening Words, and vice versa.)
How To Write Your Own Invocations
Erik Walker Wikstrom