From the beginning that has no beginning God has manifested Himself through His Messengers. Through them He causes man to know Him and to love Him; through them He breathes fresh life into creation. They are the Educators of humanity, the Source of progress, the Founders of religion. Alone and unaided, opposed by the powers of the world, each one has triumphed over adversity, unfurled the banner of His Faith and established His sovereignty over the hearts of men. Such achievements are not possible for created beings; only Manifestations of God can do these things.
In former ages the Manifestations did not explain clearly Their station. Sometimes they spoke as though They were God Himself; at others They would admit themselves human. Their immediate companions perhaps understood the hidden references to Their true station, but later followers were confused. These either worshipped them as God or regarded them only as inspired men. Doctrines such as the Trinity were evolved to try to explain the seeming contradiction of their station.
We, in this glorious age, are more fortunate. Bahá’u’lláh has revealed to us the true meaning of the paradox in words that are deep, yet crystal clear. God in His Essence, He explains, is beyond the understanding of man:
Therefore He sends His Messengers to mediate between His Essence and mankind:
These Day-Stars of divine guidance owe their great station to the Holy Spirit with which God has endowed Them. Because of it they have direct intercourse with God and act as channels for the outpouring of His grace. ‘Abdu’l-Bahá, in explaining how They mediate between God and man, likens God to the sun and the Holy Spirit to the rays of the sun bringing light and life and heat to the earth:
"As the rays of the sun bring the light and warmth of the sun to the earth, giving life to all created beings, so do the Manifestations bring the power of the Holy Spirit from the Divine Sun of Reality to give light and life to the souls of men.
Behold, there is an intermediary necessary between the sun and the earth; the sun does not descend to the earth, neither does the earth ascend to the sun. This contact is made by the rays of the sun which bring light and warmth and heat.
The Holy Spirit is the Light from the Sun of Truth bringing, by its infinite power, life and illumination to all mankind, flooding all souls with Divine radiance, conveying the blessings of God’s Mercy to the whole world. The earth, without the medium of the warmth and light of the rays of the sun, could receive no benefits from the sun.
Likewise the Holy Spirit is the very cause of the life of man; . . .” 
In another passage He likens the Holy Spirit to a mirror held to the Face of God, reflecting it for the eyes of man. To gaze directly on the Face of God is beyond man’s power, but by turning towards the Holy Spirit he can see the light of the sun reflected as in a clear mirror. Therefore Bahá’u’lláh says:
“Whoso recogniseth them hath recognised 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 tumeth away from them, has 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 everyone 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. ” 
These Mirrors are perfect Beings, who live perfect lives and give perfect teaching. There have been many of Them; Muhammad, Buddha, Moses, Jesus, Krishna, Noah, Zoroaster, Abraham, are examples. Of most we have now no record, even Their names are lost to us; but the glory which surrounds the names of those we know is itself a proof of Their divine station.
Divine, but not to be identified with the Essence of God, for that is exalted above place and time; the sun does not come down into the mirror, nor is the light of the sun the same as the sun itself. The manifestations are exalted above men, but they partake of humanity. Although possessed of the Holy Spirit, They have also a human body and a human soul. This is Their dual station, which mankind has in past ages found so confusing.
The human station of these Day-Stars of divine guidance has always been a severe test for mankind. It causes them to need food and sleep like other men, to be subject to the ills and chances of this world and to appear outwardly like ordinary human beings.
Bahá’u’lláh has written:
“As these holy Persons were subject to such needs and wants, the people were, consequently, lost in the wilds of misgivings and doubts, and were afflicted with bewilderment and perplexity. How, they wondered, could such a person be sent down from God, assert His ascendancy over all the peoples and kindreds of the earth, and claim Himself to be the goal of all creation -- . . . and yet be subject to such trivial things?” 
Sometimes the Manifestations speak in Their divine station as through with the voice of God. At others Their words stem from Their human station. Jesus spoke thus when He said: “Why callest thou me good? there is none good but one, that is, God.”  The parable of Satan tempting Jesus has been explained by ‘Abdu’l-Bahá to refer to the tempting of the Holy Spirit in Jesus by His human impulses.
The distinctions and differences between the Messengers of God originate in Their human station. In Their divine station these Great Beings are one -- one in Their perfection and one in Their Message. Bahá’u’lláh describes this unity in words of great beauty:
“lf thou wilt observe with discriminating eyes, thou wilt behold them all abiding in the same tabernacle, soaring in the same heaven, seated upon the same throne, uttering the same speech, and proclaiming the same Faith. Such is the unity of those Essences of Being, those Luminaries of infinite and immeasurable splendour!” 
In another place He puts more strongly the need to recognise Their unity:
The word of Jesus is one with the word of Moses and the word of Buddha with the word of Muhammad. Eyes directed to the perfection They share can detect no difference between these Essences of Being. They may truly claim in this station to be but one Essence speaking with but one voice. In contrast, in Their human station They are subject to the limitations of the world of creation. All created things have their own individuality and are separated one from another. Therefore Bahá’u’lláh writes:
“In this respect, each Manifestation of God hath a distinct individuality, a definitely prescribed mission, a predestined revelation, and specially designated limitations. Each one of them is known by a different name, is characterised by a special attribute, fulfils a definite mission, and is entrusted with a particular Revelation.” 
Eyes directed to differences and to the human personality of the Manifestations of God must inevitably fail to see Their inner oneness.
Failing in this, men scorn and persecute Them; so have they always treated God’s Messengers.