The religion of God has two aspects in this world

The religion of God has two aspects in this world.
The spiritual (the real) and the formal (the outward). The formal side changes, as man changes from age to age. The spiritual side which is the Truth, never changes. The Prophets and Manifestations of God bring always the same teaching; at first men cling to the Truth but after a time they disfigure it. The Truth is distorted by man-made outward forms and material laws. The veil of substance and worldliness is drawn across the reality of Truth. As Moses and Jesus brought their Message to the people, so Bahá'u'lláh brings the same Message.

Each time God sends a Great One to us we are given new life, but the Truth each Manifestation brings is the same. The Truth never changes but man's vision changes. It is dulled and confused by the complication of outward forms.
The Truth is easy to understand although the outward forms in which it is expressed bewilder the intelligence. As men grow they see the futility of man-made forms and despise them. Therefore many leave the churches, because the latter often emphasize the external only.
(Abdu'l-Baha, Abdu'l-Baha in London)