... always be unified and agreed...

Inasmuch as great differences and divergences of denominational belief had arisen throughout the past, every man with a new idea attributing it to God, Bahá'u'lláh desired that there should not be any ground or reason for disagreement among the Bahá'ís. Therefore, with His own pen He wrote the Book of His Covenant, addressing His relations and all people of the world, saying, "Verily, I have appointed One Who is the Center of My Covenant. All must obey Him; all must turn to Him; He is the Expounder of My Book, and He is informed of My purpose. All must turn to Him. Whatsoever He says is correct, for, verily, He knoweth the texts of My Book. Other than He, no one doth know My Book." The purpose of this statement is that there should never be discord and divergence among the Bahá'ís but that they should always be unified and agreed.... Therefore, whosoever obeys the Center of the Covenant appointed by Bahá'u'lláh has obeyed Bahá'u'lláh, and whosoever disobeys Him has disobeyed Bahá'u'lláh.... Beware! Beware! lest anyone should speak from the authority of his own thoughts or create a new thing out of himself. Beware! Beware! According to the explicit Covenant of Bahá'u'lláh you should care nothing at all for such a person. Bahá'u'lláh shuns such souls.

‘Abdu’l-Baha, ‘The Promulgation of Universal Peace