Knowledge is Virtue - Thoughts of Socrates

Knowledge is necessary for virtue: As per Socrates, knowledge is necessary to achieve excellence(or virtue). Be it a shoemaker, to make good shoes he must have knowledge of what good shoes are and how to make them. Similarly for life in general,  to lead a good life, one needs knowledge of what a good life is composed of.

Knowledge will definitely lead to virtue: Also if one has and truly has the knowledge of which actions make for a good life, he shall not do otherwise and shall only take actions that lead to a good life, hence signifying that knowledge will lead to virtue and attaining knowledge is attaining virtue hence, knowledge is virtue.

What is a good life?

Good life is not pleasure:
Some contemporary teachers of Socrates called 'Sophists' preached that the way to attain happiness in life is to pursue the pleasures of it. It is to gain wealth, power, fortune, etc. Sophists preached that doing these was akin to attaining virtue. 
Socrates however differed from this. 'Pleasure' cannot be the end goal of life as 'pleasure' can only coexist with pain. We pursue pleasure to avoid pain. But, we can only feel pleasure if we have pain. Hence, pleasure cannot be the end goal of life.

Man's existence as a social being:
A person is not just a self-centered individual, but a social being, a part of a community. Socrates deemed society as a natural entity and not a conventional one. 
Hence, actions that lead to betterment of the society as a whole are the actions that lead to the happiness of a person.
'Ethical life' is the answer to the means to virtue in life and knowledge of 'ethics', knowledge of the actions that a person must take leads to virtue in life.