Illusions serve the purpose they were made to serve (to make quilt real). And from their purpose, they derive whatever meaning that they seem to have.

God gave to all illusions that were made another purpose that would justify a miracle whatever form they took.

In every miracle all healing lies, for God gave answer to them all as one. And what is one to Him must be the same.

If you believe what is the same is different you but deceive yourself. What God calls one will be forever one, not separate. His Kingdom is united; thus it was created, and thus will it ever be.

The ego has a purpose, just as the Holy Spirit has. The ego's purpose is fear (to prove guilt is real)... Chap 5 Two Decisions

Vision is the means by which the Holy Spirit translates your nightmares into happy dreams...They are His substitutes for all the terrifying sights the ego's purpose brought... Chap 20 Vision of Sinlessness