وَالَّذِي حَارَتِ الْبَرِيَّةُ فِيهِ حَيَوَانٌ مُسْتَحْدَثٌ مِنْ جَمَادٍ
And that which bewildered creation is a living being brought forth from inanimate matter.
The relative expression al-ladhi harat al-bariyyatu fihi appears first and presents a mysterious subject; hayawanun mustahdathun min jamad supplies the postponed predicate. The audience wants to know what the surprising thing is.
Grammatically, al-ladhi is a relative pronoun functioning as the initial subject, harat ... fihi is its relative clause, hayawanun is the predicate, and mustahdathun its adjective. The deferred identification produces suspense.