Why is the earth mentioned with the heavens in the description of the vastness of Paradise, "as wide as the heavens and the earth," given our knowledge of its small size compared to the heavens? And is its mention in this context considered an addition to something non-existent?

The Quran's address to its audience regarding verses of creation and the universe is a clear argumentative style. This includes the mention of "the Earth," as it represents the place where humans live, and "the Heaven," due to its encompassment of humans. Thus, "the Heaven and the Earth" are a definitive logical duality that cannot be separated.

This is supported by the Almighty's saying: (All praise is due to Allah, who created the heavens and the earth and made the darkness and the light. Then those who disbelieve ascribe equals to their Lord) [Al-An'am: 1]. Indeed, Allah, Glory be to Him, paired the heavens and the earth, and darkness and light, due to their influence on humans and their connection to human life. The heavens and the earth represent the place of human dwelling, and each provides essential conditions for life.

The pairing of the heavens and the earth has been mentioned in many contexts that call for contemplation and reflection on them, even though the vastness of the heavens is further from humans. The Quran addresses humans with what they see and touch, just as there is no indication in the Quran or Sunnah that they are equal in size and expanse.

Among the contexts that necessitated the juxtaposition of the heavens and the earth is the reporting about their inhabitants, as in the Almighty's saying: (And to Allah prostrates whoever is in the heavens and the earth, willingly or unwillingly, and their shadows [as well] in the mornings and the evenings) [Ar-Ra'd: 15]; to show that the correspondence of the heavens and the earth has many aspects and does not necessarily mean their equality in size and expanse.