Explain the last commandment of Animalism: "All animals are equal."

When the animals take control of the farm and run Jones
off it, they are left to be their own masters.  The pigs emerge as the most clever of
all of the animals.  They are the ones who end up assuming the leadership of the farm. 
From the time of Old Major's death to the revolution, the Pigs had taught themselves to
read and with this, Snowball, one of the pig leaders, ends up writing/ painting the
seven commandments of Animalism, the theory that will guide the farm's governance.  The
last commandment stresses that there is to be a fundamental equality amongst all of the
animals on the farm.  This commandment highlights the idea that all animals are to be
treated fairly, with justice, and a sense of equality in all of their interactions is to
be present.  The pigs hope to stress this idea to the rest of the animals.  This seventh
commandment is one of the strongest connections to the speech Old Major gives in the
first chapter, seeking to cause change within the animals.  It is the strongest link to
the past.  It is not without irony that this last commandment, the most important in all
of its intent, is one of the first that is violated as the pigs gain greater power and
the abuses that end up coming with it.