In this speech, President Wilson is setting forth his reasons for wanting to go to war against Germany. There are two major reasons that Wilson gives for wanting war.
First, Wilson argues that the war is about democracy. He says in the speech that
The world must be made safe for democracy.
If democracy can be promoted, Wilson says, there will not longer be any reason for countries to go to war with one another. Therefore, a war for democracy is also a war to bring about world peace.
Second, Wilson talks about the need to uphold international law. He casts this war as a war against unrestricted (and illegal) submarine warfare. He casts it as a war against the violation of the rights of neutrals.
In short, Wilson says that he wants war for idealistic reasons. He wants to have an international system in which laws are respected by a world that is full of democratic countries.