What does purple refer to in Dickinson's poem "My faith is larger than the hills"?

The colour purple is normally associated with nobility and
royalty, which in the poetry of Dickinson is normally linked to the royalty of Jesus
Christ or God. Overtones of this symbolic significance of the colour purple are clear in
this poem as well, as a close examination of the first stanza indicates. Note how the
colour purple is used:

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My Faith is larger than the Hills—
So
when the Hills decay—
My Faith must take the Purple Wheel
To show
the Sun the way—

The first
stanza points towards the speaker's faith being "larger than the Hills," which means
that in the event of the destruction of those "Hills," the "Purple Wheel" must be taken
hold of by the speaker's faith in order to direct the sun on its course. That the sun's
course is associated with the "Purple Wheel" indicates the royalty and noble position of
the sun, which is personified in this poem.