Old Major's demand for change, an inversion of the current social and political order that governed the farm was vitally important. It helped to develop the belief of Animalism. This is very similar to the calls of radical change for Marx and Lenin, and the notion of inverting the traditional structure of power and the ownership of the means of production. In this light, I think that the farm changes in the elevation of animals like Napoleon and Snowball as being primarily important and being able to assert their own claims to control and power in such a setting. In an odd way, some of the concepts that stay the same is the notion of control. While the humans might have controlled the farm when Old Major demands and articulates his vision for change, the structure of power never really changed as animals replaced the corrupt tendencies of humans. Those in the position of power might have changed but the practices of government did not really change.
Every storyline needs a trigger or inciting incident. This speech set in motion the animals desire for something more. It set the stage for the purpose of a rebellion.
Animal Farm changes over time, but it is a cycle by which the animals remain in the same condition, rather, a worse condition than they were in the beginning. They sought to fulfill the vision Old Major laid out, but a power hungry leader distracts from this purpose.
Of the major tenants of the vision, we see nothing by the end of the book, but what we do see is animals convinced that something has changed even though nothing has.
In my opinion, the purpose of Old Major's vision is to get the animals to think about how badly they are being treated by the humans. Old Major thinks that there must be a better way and that animals would surely be better off if the humans were gone. So he tells them of his vision to try to motivate them to push for change.
By the end of the book, very little is still the same about Animal Farm. The pigs have taken over and are exploiting the other animals pretty badly. The only thing, in my opinion, that is consistent with Old Major's vision is that at least you do not have animals getting killed for food anymore. Other than that, the pigs are pretty much acting just like the humans did.