In making his barnstorming speech to the animals, Old Major is hoping to inspire them to rebellion against the hated human oppressor. He wants the animals to recognize their innate dignity, to understand that they're so much better than they think they are.

Through his in-depth theoretical analysis of the situation, Old Major has come to understand just how vital it is that the animals develop a revolutionary consciousness: that they see themselves as more than capable of taking hold of their own destiny and running the farm by themselves. He also knows that it is only through a vanguard of dedicated revolutionaries such as himself that the animals can be led towards a true understanding of what's in their best interests. His speech is explicitly designed for this very purpose.

A disorganized, spontaneous uprising will not succeed; the revolution must be carefully planned. But more to the point, the animals need to know just what they are and why they are rebelling before they rise up to throw off the shackles of human oppression. Hence the necessity of Old Major's speech.

Old Major's speech sets the scene for the occurrences in Animal Farm and, although it is centred around the animals own version of the Russian Revolution, it is just as much about the corruption and perversion of the ideal that later becomes symbolized by Animalism as it is about any specific persons from the Revolution.

it is Orwell’s way of suggesting that true equality never will exist.

Orwell, right from the onset, wanted to express his utter disappointment that even the Russians could not get it right and

his criticism stands against any and all totalitarian regimes.

Even at the beginning, it is apparent that "equality" is a very subjective issue and Old Major even discussed the relevance and position of "wild" creatures on the farm, relevant to the novel because it reveals - and foreshadows - the inevitable result.

The main idea therefore is that Old Major does attempt to reduce complex philosophies to something everyone can understand and is is adamant that animals cannot live together with humans - they must overthrow them.

"all the evils of this life of ours spring from the tyranny of human beings."

Old Major has a "dream," a vision 

of a society in which ...injustice is swept away and society exists in an ideal state.

His speech is a call to action.