Looking at the historical context of this talk is really important to see the significance of it. Joseph Smith was taking part in a massive theological shift.
Joseph Smith's mother, Lucy Mack Smith, was a true child of the Revolution. 4 days previous to her 1st birthday the Declaration of Independence was signed. She was in New Hampshire at the time of the signing. Her husband was only 8 days away from his 5th birthday when it was signed. So what does that have to do with the King Follet sermon? Well, a lot!
The declaration for freedom was spurred in large part by a theological shift. I can remember first reading Jonathan Edwards' most notable sermon Sinners in the Hands of an Angry God. It was sermons like these that compelled people to demand their personal liberties. It was a time we know as The Great Awakening.Less than 30 years prior to the First Vision Louis XVI was beheaded. This is significant because he was to be the embodiment of God's Kingdom on Earth. But the people were rejecting this notion. This thought out and intended act of rebellion was a symbol that the people were rejecting the idea that God had charge over their civic society,
If a religious revolution was not the end result, then it was outright atheism. Freedom became the optimism that drove people. Religion had become dogmatic and oppressive in the minds of the people. Civic freedom was the only real way to progress.
To many it seemed that the gap between freedom and religion was growing ever more wide. Everyone in the middle found themselves torn because religion demanded one way whilst the fight for freedom demanded another.
Enter Joseph Smith. When Joseph comes on stage he teaches a theology that finds harmony in both organized religion and the drive for freedom. So what became the difference? Several things mark Mormonism as "different" but in this particular case, it was the freedom and the uncapped potential. The quintessential doctrine of Mormonism thus involved man's ability to choose, or act as agents, and man's ability to progress to eventual godhood.
No longer were people torn between attempting to attach a personality to God: did he want us to be free? Or did he want us to be saved? The answer: both. And not only saved, but exalted as he is exalted! That was is his "work and glory" (Moses 1:39).
So in answer to my friend's question concerning eternal progression, I would say that this talk is the pinnacle of Mormon thought. It was such a new course in the American Theosophical landscape (and yes, theosophical is a word). It went against all of the common orthopraxy of the day because it called men to a much higher sphere. There was no longer a cap to righteousness. It implies that God is progressing (not in knowledge but in glory) and that we should be progressing. It gives a purpose to our agency and a meaning to freedom. It compels us to be more dutiful disciples.
The talk was not given in so that young missionaries could sit and speculate on who God was prior. It was meant to comfort and soothe; it was also meant to excite the mind and push the faint soul who feels that he or she just cannot make it. If they endure and do the works of Abraham (and think of all he went through) they can have the blessings of Abraham: namely godhood.
