مُّطَاعٍ ثَمَّ أَمِينٍ
Sentence structure
مُّطَاعٍ and أَمِينٍ are further genitive adjectives of the messenger; ثَمَّ is a locative adverb meaning “there.”
Ayah summary
That messenger is obeyed there and is trustworthy.
مُّطَاعٍۢ — One to be obeyed
Grammar: A Form IV passive participle and genitive adjective of رَسُولٍ.
ثَمَّ — there
Grammar: A locative adverb meaning “there.”
أَمِينٍۢ — trustworthy
Grammar: genitive adjective functioning as the adjective.