The Quran

وَآتَيناهُم بَيِّناتٍ مِنَ الأَمرِ ۖ فَمَا اختَلَفوا إِلّا مِن بَعدِ ما جاءَهُمُ العِلمُ بَغيًا بَينَهُم ۚ إِنَّ رَبَّكَ يَقضي بَينَهُم يَومَ القِيامَةِ فيما كانوا فيهِ يَختَلِفونَ

Muhammad Asad

And We gave them clear indications of the purpose [of faith];¹ and it was only after all this knowledge had been vouchsafed to them that they began, out of mutual jealousy, to hold divergent views:² [but,] verily, thy Sustainer will judge between them on Resurrection Day regarding all whereon they were wont to differ.

This, I believe, is the meaning of the phrase min al-amr in the above context, although most of the classical commentators are of the opinion that amr signifies here "religion" (din), and interpret the whole phrase, accordingly, as "of what pertains to religion". Since, however, the common denominator in all the possible meanings of the term amr - e.g., "command", "injunction", "ordinance , matter [of concern]", "event", "action", etc. - is the element of purpose, whether implied or explicit, we may safely assume that this is the meaning of the term in the above elliptic phrase, which obviously alludes to the purpose underlying all divine revelation and, consequently, man's faith in it. Now from the totality of the Qur'anic teachings, becomes apparent that the innermost purpose of all true faith is, firstly, a realization of the existence of God and of every human being's responsibility to Him; secondly, man's attaining to a consciousness of his own dignity as a positive element - a logically necessary element - in God's plan of creation and, thus, achieving freedom from all manner of superstitions and irrational fears; and, lastly, making man aware that whatever good or evil he does is but done for the benefit, or to the detriment, of his own self (as expressed in verse 15 above).
See 23:53 and the corresponding note 30.