The Center of the Covenant
After Bahá'u'lláh's passing, Abdu'l-Bahá became the Center of the Covenant, the sole authorized interpreter of the teachings.
Bahá'u'lláh's Will and Testament explicitly appointed Abdu'l-Bahá as the Center of the Covenant and sole interpreter of the Bahá'í writings. This unique arrangement has preserved the unity of the Bahá'í Faith where other traditions have fragmented. The covenant creates an unbroken line of authorized interpretation.
Turn to Abdu'l-Bahá. Whatever he says is correct.
The explicit appointment of a successor-interpreter is unique in religious history and has had profound consequences for Bahá'í unity.
Kitáb-i-'Ahd