It is evident that, for all of his faults, Bahá’u’lláh had no lack of self-esteem:

Would ye laugh to scorn and contend with Him, a single hair of Whose head excelleth, in the sight of God, all that are in the heavens and all that are on the earth?
—Suriy-i-Haykal (Sura of the Temple)

This passage helps us to understand why Bahá’u’lláh let his hair grow so wildly, in spite of forbidding long hair in his book of laws.

This “Sura of the Temple” is also known as the “Sura of the Body”.

John Walbridge writes:

In the Súratu’l-Haykal the primary sense of haykal is the human body, particularly the body of the Manifestation of God, …

Adib Taherzadeh reported in Revelation of Bahá’u’lláh that Bahá’u’lláh wrote that he was both the author and the addressee of this Tablet. We can almost hear Bahá’u’lláh crying into the reflection pool, “make Me to be thine Idol!”

For more information, see Tablet of the Temple by Jonah Winters.