Today, the most important affair is firmness in The Covenant, because firmness in The Covenant wards off differences.
In former cycles no distinct Covenant was made in writing by the Supreme Pen; no distinct personage was appointed to be the Standard differentiating falsehood from truth, so that whatever he said was to stand as truth and that which he repudiated was to be known as falsehood. At most, His Holiness Jests Christ gave only an intimation, a symbol, and that was but an indication of the solidity of Peter's faith. When he mentioned his faith, His Holiness said, 'thou art Peter’ - which means rock - 'and upon this rock will I build my church.' This was a sanction of Peter's faith; it was not indicative of his (Peter) being the expounder of the Book, but was a confirmation of Peter's faith.
But in this Dispensation of the Blessed Beauty (Baha’u’llah) among its distinctions is that He did not leave people in perplexity. He entered into a Covenant and Testament with the people. He appointed a Center of the Covenant. He wrote with His own pen and revealed it in the Kitab-i-Aqdas, the Book of Laws, and Kitab-i-Ahd, the Book of the Covenant, appointing him (‘Abdu’l-Baha) the Expounder of the Book. You must ask him (‘Abdu’l-Baha) regarding the meanings of the texts of the verses. Whatsoever he says is correct.
Outside of this, in numerous Tablets He (Baha’u’llah) has explicitly recorded it, with clear, sufficient, valid and forceful statements. In the Tablet of the Branch He explicitly states: “Whatsoever the Branch says is right, or correct; and every person must obey the Branch with his life, with his heart, with his tongue. Without his will, not a word shall anyone utter.” This is an explicit text of the Blessed Beauty. So there is no excuse left for anybody. No soul shall, of himself, speak anything. [The words must be according to what has proceeded from the Mouth of the Will of God and is recorded in Tablets.] Whatsoever his (‘Abdu'l-Baha's) tongue utters, whatsoever his pen records, that is correct; according to the explicit text of Baha’u’llah in the Tablet of the Branch.