In "The Wonderful Wizard of Oz," why does the Good Witch of the North advise Dorothy to go to the Emerald City?

Question

In the novel by L. Frank Baum, the Good Witch of the North does not know how Dorothy can get back to Kansas, so she uses her magic to conjure a chalkboard with instructions for Dorothy to go to the Emerald City.

The following quotation highlights this:

As for the little old woman, she took off her cap and balanced the point on the end of her nose, while she counted “One, two, three” in a solemn voice. At once the cap changed to a slate, on which was written in big, white chalk marks:

“LET DOROTHY GO TO THE CITY OF EMERALDS”

The little old woman took the slate from her nose, and having read the words on it, asked, “Is your name Dorothy, my dear?”

“Yes,” answered the child, looking up and drying her tears.

“Then you must go to the City of Emeralds. Perhaps Oz will help you.”

My question is: why does the chalkboard instruct Dorothy to go to the Emerald City when the silver shoes are capable of sending her home? Is this chalkboard all-knowing? If so, why send Dorothy on a wild goose chase? And if it is not all-knowing, where do you suppose it got this advice from?

Answer 1

I don't think there's really an answer, but there is a plausible guess.

The spirits told her to

The Good Witch's magical chalkboard seems to recall the practice, common among spiritualists and mediums of the 1800s, of supposedly receiving ghostly communications written on slates.

From the link:

Friday, 14th December 1877 (11.0 to 11.40 A.M.). Today, first one of the slates kept always in readiness, which I myself selected and cleaned, was laid open with a bit of slate-pencil upon the floor under the table. Now, while Slade had both his hands linked with ours upon the table, and his legs, turned sideways, were continually visible, writing, loudly perceptible by us all, began on the slates lying below. When we raised it, there were on it the words—‘Truth will overcome all error!’

Although Frank Baum published The Wonderful Wizard of Oz in 1900, he was born in 1856, and thus had probably heard of mediums doing such things (the practice did not fall out of favor for several decades).

In other words, there may be nothing magical about the chalkboard (except that the Witch produced it from a hat). It is merely a tool to allow her spirit helper to give her advice.

The Good Witch is presumably receiving a communication from a spirit or ghost helper, which, although wise, does not know everything.