In one place, he says, that it means Mohammad (s) is the final Nabi just as he Mohammad (s) is the first Adam (a) and that all Prophets (a) are each other type meaning.
In another place, he says, it means he is the final one in the old cycle before the new cycle of creation.
This is a contradiction.
Baha'u'llah offers a much deeper understanding of why Muhammad is called "Seal of Prophets"
He reveals the secret of God.
Baha'u'llah explains in Ighan, that, in each Age, God stirred up 'commotion'.
He gives examples. He narrates the story of Moses, that how Moses ended up killing a man, and therefore had to flee. Once He came back to people, He was known as a person who committed Murder. So, when Moses claimed that, God spoke to Him, and made Him a Messenger, this was very difficult for people to accept Him, because He was already known as a Murderer among people. After all, Who was going to believe that a Murderer, who fled, who was raised in the household of Pharaoh, the tyrant king, can be really the God's Messenger?!!!!
Baha'u'llah then says:
"Was not God, the omnipotent King, able to withhold the hand of Moses from murder, so that manslaughter should not be attributed unto Him, causing bewilderment and aversion among the people?"
Baha'u'llah then goes on, and gives another example. This time about Jesus.
He narrates the story of how Mary, mother of Jesus got pregnant without being married first. This caused people to think of Mary, as an adulterous.
Really, after all, in those days, who was going to believe the story and claim of Mary, that she got pregnant by the Holy Spirt?!!!
One should try to put himself in her place to get the feeling of the situation!
Now, once Jesus was born, therefore, He became known among people, as an illegitimate child. Thus, some years later, when He claimed to be the Messenger of God, People had much more difficulty to accept His claim. After all, someone who in their sight was an illegitimate child whose mother was known as adulterous, claimed to be the Messenger of God!!!
One can immagine, that It must have been obvious to them, He was a liar, just like His adulterous mother!
Baha'u'llah explains, these things happend only, and only according to the Will of God, to stir up commotion.
"And now, meditate upon this most great convulsion, this grievous test. Notwithstanding all these things, God conferred upon that essence of the Spirit, Who was known amongst the people as fatherless, the glory of Prophethood, and made Him His testimony unto all that are in heaven and on earth.
Behold how contrary are the ways of the Manifestations of God, as ordained by the King of creation, to the ways and desires of men! "
Meaning, God's will has been to create, a type of difficulty and barrier for the people at the Time of every Messenger, so, only those who truly investigate the Truth, and make an effort for God, may become successful in recognition of His Messenger.
I think of it, as creating a mechanism that Tests and Separates those who want to find easy reason to disbelieve from those who look and search after God in truth and sincerely.
There must be a difference between sincere ones and those whose heart has disease.
This way, Those who look for excuses and want to disbelieve, can find an easy way to reject, and be in the Hell, they choose for themselves.
Remember, only those who make an effort for God, must be guided!
وَٱلَّذِينَ جَـٰهَدُوا۟ فِينَا لَنَهْدِيَنَّهُمْ سُبُلَنَا ۚ
Quran 29:69
Then Baha'u'llah goes on, and explains, this has been always the way of God. God creates a barrier, to separate those who truly make an effort for God, so, only they may be guided, and the rest, go astray.
Bahaullah then explains, Likewise, For this Age, God did this, by designating Muhammad as "Seal of Prophets", creating a commotion For the people of this Age.
God did so, to Create a false idea that, there won't be another Revelation after Muhammad. this was the Barrier this time, to test those who make an effort for God. (just as how He created false idea that Jesus was illegitimate).
Thus, Creating a obstacle or a Mechanism that Separates those who want to easily disbelieve from those who make an effort, and search after God. One needs to pass from this Obstacle to find the Right Path.
Thus, according to Baha'u'llah, the main Purpose of God, for designating Muhammad as "Seal of Prophets" was to create this Obstacle, that causes the disbelievers to think, that Muhammad is the Final.
Baha'u'llah explains:
"The mystery of this theme (Seal of Prophets) hath, in this Dispensation, been a sore test unto all mankind. Behold, how many are those who, clinging unto these words (Seal of Prophets), have disbelieved Him Who is their true Revealer."
Baha'u'llah goes on and explains, this is how God creates "Veils", so, the truth may not be seen, easily, unless one makes a true effort to remove the veil:
"Furthermore, among the “veils of glory” are such terms as the “Seal of the Prophets” and the like, the removal of which is a supreme achievement in the sight of these baseborn and erring souls. "
Have you heard, God has thousands of veils, and on the Day of Resurrection, disbelievers cannot see Him?
But the reality is that, this term "Seal" can have different meanings, and only God, Himself can claim what He meant by it. (Quran 3:7). To insist that one knows what it means, is yet failing another test of God! Did not God say, only He knows its interpretation? 3:7
Is my explanation clear to you so far?
If you want to understand Baha'u'llah's explanation of "Seal of Prophets", you must first understand what I tried to explain here. Without that, it is not possible.