The ancients knew more than we do today. Most moderns view freedom as “the ability to do whatever I want whenever I want.” Yet through his dialogues in The Republic, Plato describes the Tyrant, the person with the power to do whatever he wants, as a slave, unable to escape his base desires.
As a Christian, I don't wholly agree with the Stoics, but there is a lot of overlap. Stoicism was the predominant philosophy during the Roman Empire's conversion, and I appreciate the philosophical foundation they built for virtue ethics.