Guru Vachaka Kovai

It is only Self, the one pure knowledge, that, as the unreal knowledge [the mind], makes all differences [vikalpas] appear. Therefore for the one who knows and reaches Self, which is the harmonious knowledge, all those other things [the entire world-appearance] will be [found to be] of the nature of the one Self.

—

Guru Vachaka Kovai (The Garland of Guru’s Sayings) by Sri Muruganar - Ch. All is Brahman, Verse 985

All differences such as name and form, time and space, subject and object, are made to appear only by the mind, which is truly non-existent, being nothing but an unreal appearance in the real Self.

Just as when the real rope is seen, the unreal and non-existent snake is found to be nothing but that rope, so when the real Self is known, the unreal and non-existent mind and all its products (the entire world-appearance) are found to be nothing but that Self. It is only in this sense that the unreal world-appearance is said to be of the nature of the one Self or Brahman.