With this paragraph, Baha'u'llah is really moving into His main argument in Part One of this Book. He has already established the lineage of Messengers we acknowledge, and shown us what They have in common.
Now He is beginning to show another common point They have, which the reader will already acknowledge, namely that They have promised another Messenger to come. At the same time, He reminds us that we are "endowed with understanding", and that this is praiseworthy. Endowed, just to remind us, means to furnish or to bestow with talent. This, obviously, comes from God.
Also, if this is the model by which we are to teach the Faith, then we feel there is a lesson here. At no point does Baha'u'llah hint that what the reader believes is wrong. He shows the reader what he already knows, agreeing all the way. Step by step He carefully strips away any veils and shows what is truly important. He puts it all into a logical order so that each step makes a clear sense.
Just what is it He is pointing out? He is reminding us that all the Messengers have promised another Messenger to follow. But in doing so, Baha'u'llah also shows us more about Jesus and His life. He first points out that it was the "fire of the love of Jesus" that burned away the veils. It was neither His teachings nor His arguments. It was His love.
It reminds us of the story of 'Abdu'l-Baha in which the first pilgrims from the West were with Him, and they were to go to Mount Carmel for a meeting. But, unfortunately, May Maxwell was ill, and 'Abdu'l-Baha said that they would not have the meeting that day. He said that they could not leave behind one of the beloved of the Lord, for "We could none of us be happy unless all the beloved were happy." This concern, this love for each one of them was so characteristic of Him. As May writes, "It was so contrary to all ordinary habits of thought and action, so different from the life of the world where daily events and material circumstances are supreme in importance that it gave us a genuine shock of surprise, and in the shock the foundations of the old order began to totter and fall." This was one instance in which the Master gave the friends a vision "of that infinite world whose only law is love".
Getting back to Jesus, once that was done and His station, or authority, was proven, Jesus then began the work of preparing His disciples for His passing. It makes sense, of course, for if His station were not established then the "fire of bereavement" would not be as intense.
There is such a close tie between this fire of love and the fire of bereavement that we felt it worth mentioning. The greater the love, the greater the grief. It is like when Baha'u'llah says in The Seven Valleys that the steed of the Valley of Love is pain.
But here, in this paragraph, the two quotes that Baha'u'llah put here are well-known to the reader, and the Uncle of the Bab, to whom this was addressed, no doubt recognized them as referring to Muhammad. But remember, Baha'u'llah has already been demonstrating the similarities between the Messengers. Jesus' promises fulfilled in Muhammad becomes the template by which the Bab fulfills the promises of Muhammad.
We find it interesting that Baha'u'llah uses the term "the Revealer of the unseen Beauty" when referring to Jesus. Why? What does this term mean? As usual, we're not sure, but we think of it in a couple of different ways. First, Baha'u'llah mentions that the the fire of Jesus' love burned away some veils. Veils obscure our vision. By burning away these veils, we were better able to see God and the world around us. Jesus revealed this beauty to our eyes. He also revealed the beauty of His own Self.