Aalaa’ — wondrous acts of power
The question directs us to be in awe, not in denial, of Allah’s wondrous acts of power.
Ayah 55:21 — Presentation
فَبِأَيِّ آلَاءِ رَبِّكُمَا تُكَذِّبَانِ
“Then, which of the Aalaa’ (wondrous acts of power) of the Lord of both of you will you both deny/declare to be false/dismiss/undermine?”
The question directs us to be in awe, not in denial, of Allah’s wondrous acts of power.
Allah has separated the nations of the world by land mass.
Through this division, power between human beings becomes divided so that one power cannot dominate over everything.
Allah is holding the world together from falling into chaos in just the way He divided the seas.
According to the main opinion of the Mufassireen, this refers to Allah having divided the fresh waters from the sea waters and created a barrier between them where they meet but do not mix.
Then the focus of this Ayah would be upon this amazing sign of Allah’s power and capability to create such a reality.
Division of lands distributes human power; the divided seas illustrate His power. Both call us away from denial and toward recognition of His ordering of creation.