There, Baha'u'llah warned them that God's acceptance of their pious deeds is dependent on their belief in Him. It is not at all obvious that Baha'u'llah would have seen a tremendous ethical difference between following the laws of one religion over following the laws of another. Baha'u'llah was thoroughly repelled by the obsession with religious minutiae characteristic of Islamic law. Prayer is important. Fasting is important.
Cleanliness is important.
Whether a mouse falling into your cistern makes your ablutions invalid is not important. An indication of this is the palpable lack of enthusiasm that Baha'u'llah showed for promulgating laws. The perfection of the supremacy of man is in faith in God. This will be corrected to 'everyone' in the next printing. Baha'u'llah denies the Pauline and Shi'ite doctrine of justification by faith alone.