Here's the passage that first alerted me to trouble. Read carefully, there is a quiz at the end.
"And we're not alone, you know children [in the fight against evil], came Mrs. Whatsit, the comforter. "All through the universe it's being fought. . . You think about that, and maybe it won't seem strange to you that some of our very best fighters have come right from your own planet, and it's a little planet, dears, out on the edge of a little galaxy. You can be proud that it's done so well.
"Who have our fighters been?" Calvin asked.
"Oh, you must know them dear," Mrs. Whatsit said. . .
"Jesus!" Charles Wallace said. "Why of course, Jesus."
Of course Mrs. Whatsit said, "Go on, Charles, love. There were others. All your great artists. They've been lights for us to see by."
"Leonardo da Vinci," Calvin suggested tentatively, "And Michelangelo?"
"And Shakespeare," Charles Wallace called out "And Bach! And Pasteur and Madame Curie and Einstein!" pg. 88-89
The problem with the passage displayed above is
a) Jesus did not come from earth
b) There were no "others" like Jesus
c) A Guardian Angel would never stoop to the nickname "Mrs. Whatsit"
d) all of the above