What was the purpose of Old Major's vision in Animal Farm? How does Animal Farm change? Do any concepts of the vision stay the same?

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.