Bahá’u’lláh wrote:

“The door of the knowledge of the Ancient Being hath ever been, and will continue for ever to be, closed in the face of men. No man’s understanding shall ever gain access unto His holy court. As a token of His mercy, however, and as a proof of His loving-kindness, He hath manifested unto men the Day Stars of His divine guidance, the Symbols of His divine unity, and hath ordained the knowledge of these sanctified Beings to be identical with the knowledge of His own Self. Whoso recognizeth them hath recognized God. Whoso hearkeneth to their call, hath hearkened to the Voice of God, and whoso testifieth to the truth of their Revelation, hath testified to the truth of God Himself. Whoso turneth away from them, hath turned away from God, and whoso disbelieveth in them, hath disbelieved in God. Every one of them is the Way of God that connecteth this world with the realms above, and the Standard of His Truth unto every one in the kingdoms of earth and heaven. They are the Manifestations of God amidst men, the evidences of His Truth, and the signs of His glory.”
(Gleanings from the Writings of Bahá’u’lláh, p. 49-50)

“These sanctified Mirrors, these Day Springs of ancient glory, are, one and all, the Exponents on earth of Him Who is the central Orb of the universe, its Essence and ultimate Purpose. From Him proceed their knowledge and power; from Him is derived their sovereignty. The beauty of their countenance is but a reflection of His image, and their revelation a sign of His deathless glory. They are the Treasuries of Divine knowledge, and the Repositories of celestial wisdom. Through them is transmitted a grace that is infinite, and by them is revealed the Light that can never fade… These Tabernacles of Holiness, these Primal Mirrors which reflect the light of unfading glory, are but expressions of Him Who is the Invisible of the Invisibles. By the revelation of these Gems of Divine virtue all the names and attributes of God, such as knowledge and power, sovereignty and dominion, mercy and wisdom, glory, bounty, and grace, are made manifest.”
(Gleanings from the Writings of Bahá’u’lláh, p. 47-48)

‘Abdu’l-Bahá said:

“All the perfections, the bounties, the splendors which come from God are visible and evident in the Reality of the Holy Manifestations, like the sun which is resplendent in a clear polished mirror with all its perfections and bounties. If it be said that the mirrors are the manifestations of the sun and the dawning-places of the rising star, this does not mean that the sun has descended from the height of its sanctity and become incorporated in the mirror, nor that the Unlimited Reality is limited to this place of appearance.”
(Some Answered Questions, p. 147-148)