It might seem trivial, but the definition of those words is important. They're the slogan of the French Revolution. I got Liberty and Equality, but "Fraternity" always escaped me. Fraternity? What the hell does that mean? What does it have to do with Liberty and Equality? As it turns out, the meaning of Fraternitie is "Brotherhood", literally. Frater=Brother in Latin, so Fraternitie means something like Brother-ness in the literal rendering.
Liberty, Equality, and Brotherhood. That makes sense. I guess it's important in that it sheds light on the thought of the French Revolution and makes it less abstract than it might be otherwise. After all, "Brotherhood" is something else besides a pure deduction from first principles.
Another reason why "Brotherhood" is so important is that the sentiment was part of the redefinition of people living in France from subjects of the King of France to French Citizens.