Why did Baha’u’llah bear such incredible ordeals, calamities and sorrows?

... the Blessed Perfection bore all these ordeals and calamities in order that our hearts might become enkindled and radiant, our spirits be glorified, our faults become virtues, our ignorance be transformed into knowledge; in order that we might attain the real fruits of humanity and acquire heavenly graces; in order that, although pilgrims upon earth, we should travel the road of the heavenly Kingdom, and, although needy and poor, we might receive the treasures of eternal life. For this has He borne these difficulties and sorrows. 

- 'Abdu'l-Baha  (From a talk; ‘The Promulgation of Universal Peace: Talks Delivered by 'Abdu'l-Bahá during His Visit to the United States and Canada in 1912’)

Baha’u’llah’s last outstanding Tablet

We are told by the beloved Guardian that the Epistle to the Son of the Wolf is "the last outstanding Tablet revealed by the Pen of Bahá'u'lláh."- (Shoghi Effendi, ‘God Passes By’)

Shoghi Effendi gave the western believers his fifth and last book of translations of the Writings of Bahá'u'lláh, undertaken during the winter of 1939-40 … The Epistle to the Son of the Wolf was Bahá'u'lláh's last major work and contains a selection from His own Writings made by Himself (surely a unique occurrence in religious history!) during the last two years of His life and has therefore a special position of its own in the literature of our Faith. In a cable shortly prior to its publication Shoghi Effendi said "Devoutly hope its study may contribute further enlightenment deeper understanding verities on which effective prosecution teaching administrative undertakings ultimately depend..." 

- Ruhiyyih Khanum  (‘The Priceless Pearl’)

1848: Bahá’u’lláh was placed in confinement in ‘Amul

When… We went to Ámul, [December 1848] such was the turmoil which the people had raised that above four thousand persons had congregated in the masjid and had crowded onto the roofs of their houses. The leading mullá of the town denounced Us bitterly… We informed him that, although We had never met Him face to face, yet We cherished, none the less, a great affection for Him. We expressed Our profound conviction that He had, under no circumstances, acted contrary to the Faith of Islám.

The mullá and his followers, however refused to believe Us, and rejected Our testimony as a perversion of the truth. They eventually placed Us in confinement, and forbade Our friends to meet Us. The acting governor of Ámul succeeded in effecting Our release from captivity. Through an opening in the wall that he ordered his men to make, he enabled Us to leave that room, and conducted Us to his house. No sooner were the inhabitants informed of this act than they arose against Us, besieged the governor’s residence, pelted Us with stones, and hurled in Our face the foulest invectives. 

- Baha’u’llah  (Quoted by Nabil in ‘The Dawn-Breakers’; translated and edited by Shoghi Effendi)

When Bahá’u’lláh’s father died the Government wished Him to succeed to his position in the Ministry

When Bahá’u’lláh was twenty-two years old, His father died, and the Government wished Him to succeed to His father’s position in the Ministry, as was customary in Persia, but Bahá’u’lláh did not accept the offer. Then the Prime Minister said: “Leave him to himself. Such a position is unworthy of him. He has some higher aim in view. I cannot understand him, but I am convinced that he is destined for some lofty career. His thoughts are not like ours. Let him alone.” 

- ‘Abdu’l-Baha  (Quoted in ‘Baha'u'llah and the New Era’, by Dr. J.E. Esslemont)

The “ominous warning sounded by Bahá’u’lláh” concerning the plight of humanity

“Bestir yourselves, O people,” is, on the one hand, the ominous warning sounded by Bahá’u’lláh Himself, “in anticipation of the days of Divine Justice, for the promised hour is now come.” “Abandon that which ye possess, and seize that which God, Who layeth low the necks of men, hath brought. Know ye of a certainty that if ye turn not back from that which ye have committed, chastisement will overtake you on every side, and ye shall behold things more grievous than that which ye beheld aforetime.” And again: “We have fixed a time for you, O people! If ye fail, at the appointed hour, to turn towards God, He, verily, will lay violent hold on you, and will cause grievous afflictions to assail you from every direction. How severe indeed is the chastisement with which your Lord will then chastise you!” And again: “God assuredly dominateth the lives of them that wronged Us, and is well aware of their doings. He will most certainly lay hold on them for their sins. He, verily, is the fiercest of Avengers.” And finally: “O ye peoples of the world! Know verily that an unforeseen calamity is following you and that grievous retribution awaiteth you. Think not the deeds ye have committed have been blotted from My sight. By My Beauty! All your doings hath My pen graven with open characters upon tablets of chrysolite.” 

- Shoghi Effendi  (‘The Promised Day Is Come’)

An illuminated Seal of Baha'u'llah