Washington's farewell address was important for a number of reasons. Often overlooked is the fact that, like many of his actions, he set the precedent for a Presidential farewell address.
Beyond that, he had two warnings for the nation in his parting speech. First, he pleaded with his new nation to avoid the engaging in standing alliances with European powers. American could not afford to become embroiled in a conflict unless it was in our best interest, not just for the sake of an alliance. His second area of concern was with political parties. Washington was highly opposed to the formation and function of such groups, and felt America would suffer at their hands.
The United States heeded Washington's warning about entangling alliances well into the twentieth century; however, his concerns about political parties were immediately ignored as those groups would quickly shape the face of American politics.