First, I would like to begin with a question. Why is it called the Encomium on Helen when it could be the Encomium to Theseus?
In praising Theseus, Isocrates hopes to accomplish a dual purpose. First, he seeks to establish the practically of wisdom. He seeks to show that all human acts should be of practical use to humans, and that only a proper education in practical wisdom can achieve this. Second, he seeks to establish a syllogism that will help strengthen the foundation of his argument. His syllogism is basically as follows, in my view:
Theseus is the greatest hero.