وَذٰلِكَ حَقِيقَةُ التَّصْدِيقِ عَلَى مَا مَرَّ
This is connected to the reality of assent already established.
Sincere faith accepts the truth and authority of God's message. Accidentally acting in the same way as a religious command, while denying that command's authority, is not the same as obeying it in faith.
Yet assent and bodily action are not simply interchangeable concepts. The former concerns accepting a truth inwardly; the latter includes duties and visible manifestations which follow from that acceptance. The account therefore joins genuine belief and submission without erasing the distinction between their descriptions.