The exact meaning of invoke can depend upon its context. For example:
"invoking God's help"; or "invoking the spirit of the dead" — to call upon a great or magical power
"I invoke the First Amendment"; or "I invoke the words of Thomas Jefferson" — to cite or call upon for validation
"She invoked his sympathy and family memories." — to call upon someone's feelings or memories
"She invoked his assistance." — to call earnestly for
"The program invokes the subroutine" — to call up a computer program
And the fetish most treasured by mothers, against dysentery, contains a particle of all the things invoked by the word nzolo: you must dig and dry the grub and potatoes, bind them with a thread from your wedding cloth, and have them blessed in a fire by the nganga doctor.
Book 5 — Exodus (99% in)
There are no more uses of "invoke" in The Poisonwood Bible.