The earliest extended stoic text to survive the passage of time is a hymn to Zeus. It was written by Cleanthes, the second head of the school, in the third century BCE. The mighty god is summoned as "most glorious of the immortals, invoked by many names, ever all-powerful".

But it is not just a hymn of high praise. Within it threads the fundamental element of stoic thought that underpins the exercises and practices, psychology and cosmology celebrated this week by the organisers of Stoic Week. Without this thread, Cleanthes felt that stoicism makes no sense and, worse, might lead you astray.

It was called the logos – using one of those extraordinarily rich Greek terms that can be translated as word, discourse, reason, activity and principle. The logos, Cleanthes remembers, "moves through all creation". It is the wellspring of unity, direction, purpose. The wretched flee the logos, he continues, and their alienation from it is the cause of their suffering. Because they do not know the logos in their lives they instead seek fame, money, pleasure for pleasure's sake, all manner of passing things that sweep them along and actually destroy what human beings truly wish for. The result is a troubled life of ignorance. "If they obey [the logos] intelligently, they would have the good life," the hymn continues.

It is striking, then, that Stoic Week makes no reference to the logos (unless a moment of revelation has yet to come on the blog). Presumably that is because the philosophers and therapists behind the experiment feel either that the theological aspect is irrelevant today or that it would distract from the usefulness of the stoic practices that aim to build resilience, gratefulness and aspiration. But I think it is a vital issue to raise.

The ancient stoic training was an attempt to orient the whole of life to the logos. Chrysippus, the third head of the school and one of the most brilliant philosophers of the ancient world, used the metaphor of a cylinder rolling down a hill. Life is like that. There is nothing you can do to change it. What you can do is learn "to go with the flow", as opposed to resisting the bumps and shocks.

But why should you go with the flow, one of his young disciples might have asked? Because the flow can be trusted, Chrysippus would have replied. It is the action of the logos. It is mysterious, yes; often painful, yes. But ultimately benign. And if life were not providential, you are right: it would be more noble to resist it all the way.

In other words, the stoic notion of flow was a kind of devotion, an offering of yourself. Cultivating the right inner attitude was absolutely crucial to the good life stoicism promised. Practise stoicism for self-serving reasons, as instrumentally driven therapies and self-help might encourage, and you risk alienating yourself further.

Think about it this way. It is often remarked that ancient stoicism is close to modern CBT. That undoubtedly offers people timely help. But only some, it seems. Longitudinal testing of CBT appears to be suggesting the benefits are short-lived. I wonder whether Chrysippus might help explain why: does CBT unwittingly encourage the delusion of living out of your own strength, he might ask?

Stoicism was the most successful of the ancient Athenian schools. What is perhaps not much appreciated now is that it is, in a way, alive and kicking to this day. When the first Christians searched for resources to try to understand what they had encountered in the life and death of Jesus of Nazareth, stoic insights made tremendous sense.

St Paul felt that his experience of the divine was like that of the stoics. "For in him we live and move and have our being," he taught, explaining he was quoting from stoic philosophers. St John was so impressed that he argued Jesus was the incarnation of the logos, celebrated in the opening line of his gospel: "In the beginning was the word." Practices such as saying grace before meals, or giving thanks for the day at night-time, are stoic.

Is it too cheeky to suggest that if you want to practise stoicism today, you might start in a church?