The lyrics of the song are full of inspiration. They envision a better future for the animals. We learn that the animals experience the "wildest excitement" from hearing the song, and even the least intelligent of them can sing a few words of it. The most intelligent animals learn it by heart in a few minutes. This suggests the lyrics are catchy and easy to learn.
The song first talks about a "golden future" in which humans will be overthrown and the animals will no longer be under their control. Riches will come to the animals, the song says, especially in the form of plentiful food. However, the end of the song reminds them that they have to be willing to risk everything for this vision to become reality:
For that day we all must labour,
Though we die before it break;
Cows and horses, geese and turkeys,
All must toil for freedom's sake.
The song primes the animals for struggle and sacrifice to achieve their goals and therefore inspires them to risk their lives for the cause. We learn that they sing it every time they have a secret meeting, so it is constantly fresh in their minds.