This is where my thoughts come from, in this explanation, it is explained that the negation is connected to past broken Covernants and how in this dispensation, the Covernant is protected by the affirmation.
".. In the
Tablet of Salmán Bahá'u'lláh explains one of the most interesting mysteries in the
Qur'án, a mystery which had hitherto remained unnoticed. He refers to the well-known phrase, 'There is no God but Him'. This is the cardinal statement of faith which every Muslim must make, and which is the basis of the Islámic religion.
As we have previously written,* the Word of God has many significances which are beyond the ken of men. There are inner meanings enshrined in the Word of God which only His Manifestation and those whom He guides understand. Bahá'u'lláh explains that in this phrase 'There is no God but Him', the letter of negation precedes that of affirmation. Therefore as a result of the creative influence of this phrase, ever since it was revealed, the violators of the Cause of God, representing the letter of negation, dominated over the faithful in the past. All the sufferings which the hands of the breakers of the Covenant of God inflicted upon the steadfast Muslims and their apparent superiority, were the fulfilment of the Words uttered by Muhammad. God had, through His wisdom, so destined that those who were impure and rebellious should dominate those who were true and sincere.... "
"... Referring to the fore-mentioned phrase 'There is no God but Him', Bahá'u'lláh, in the
Tablet of Salmán, proclaims in majestic and powerful language that He has removed the letter of negation which had been placed before that of affirmation. This phrase, which the Prophet of Islám, through His all-encompassing wisdom, regarded to be the cornerstone of His Faith, is now, in the Dispensation of Bahá'u'lláh, symbolically replaced by the affirmative phrase 'He is God', signifying that the Revealer of the Cause of God holds within His hands the reins of authority, and, unlike the Dispensations of the past, no one has the power to wrest it from Him. The violators and the breakers of Bahá'u'lláh's Covenant, as history has shown, have been utterly impotent to introduce divisions within His Faith, to arrest its onward march or influence its glorious destiny.... "
So it is from this following passage of the writings of the Bab, that has given us much to consider. I see we one and all still struggle to understand the Station of the Messenger, we now know they are not God in Essence, but I think this passage tells us that the Messenger is all we will ever know about God.
Read it here:
https://reference.bahai.org/en/t/tb/SWB/swb-2.html
Extract
"....... He is the Most Glorious.
HE is God, no God is there but Him, the Almighty, the Best Beloved. All that are in the heavens and on the earth and whatever lieth between them are His. Verily He is the Help in Peril, the Self-Subsisting.
This is a letter from God, the Help in Peril, the Self-Subsisting, unto God, the Almighty, the Best Beloved, to affirm that the Bayán and such as bear allegiance to it are but a present from me unto Thee and to express my undoubting faith that there is no God but Thee, that the kingdoms of Creation and Revelation are Thine, that no one can attain anything save by Thy power and that He Whom Thou hast raised up is but Thy servant and Thy Testimony...... "
Regards Tony