For Epicurean though there is no higher force than human intellect in itself, and it is intellect that arranges things according to its own desires. Atoms can be deflected from their causal pathways by human willpower. It is also much easier to destroy existing arrangements of material atoms than to create new ones, so one has to be careful engaging with life, yet ultimately these atoms will prevail in their perpetual movement which has no purpose and no meaning, except endless causality principle, dominating the nature of things. People can interfere with this endless flow, but perhaps better not. Gods are somewhere up there, immortal beings living on another planet, and one true philosopher may observe them and wisely take them as an example of perfectly virtuous and pleasurable life close to Nature, but that's all, folks. Gods may be also easily dispensed with, in case one does not wish to see them, as they have no real power over this realm. It is perfectly good and even better to worship and follow an example of Epicurus himself as a God on Earth, revealed through his own and his followers writings, instead of seeking Zeus blessing via ancient and largely ignorant cults.
Stoicism in its classic form is surprisingly close to Christianity, with its fundamental belief in universal Logos, which arranges the whole Nature in rational and balanced way, and a philosopher has find his purpose according to this rational arrangement and follow it, ultimately pursuing fulfillment and good life within society (we are social animals).
Human intellect is not above all things, but subservient to Logos, and a true philosopher has no license to invent explanatory truths at whim, as Epicurus was so keen to be doing, no matter how plausible they feel, but has to discover the singular Truth that is already up there and not necessarily among events and objects immediately accessible to our perception.
According to Logos, every human being, and philosopher in particular, has a special, albeit perfectly natural purpose, and it is a philosopher not only to discover and follow his own duty, but to help his friends to fulfill their duties as well. Far from contemplative stance of Epicureans, Stoics argue for active participation in social life, although they advise against mingling with the crowd and any sort of showing off. Life can be viewed from various angles - as a trip on a boat, as a theatrical play or as a dinner party, but in any case, every fellow traveler and every participant has a job to do and task to fulfill. All this flows naturally from a belief in sort of Providence. Gods are higher beings who's powerful influence on our lives a true philosopher may perceive directly, like Marcus Aurelius states, so piety seems to be a wise choice rather than a whim.
It is rather easy to deduce from Seneca and Marcus Aurelius texts, that if one chooses not to see gods will and not to follow Logos in a discovery of truth, he is not a free and wise man according to Stoics, but merely a blind arrogant fool, stumbling awkwardly while trying to maintain some semblance of composure.
I am highlighting the differences without paying homage to similarities between these two schools of though. Yet the similarities between school of Epicureans and Stoics are all well known and repeated many times, i.e. the accent on moral value of self-control and moderation, while the differences are obfuscated.
Again, curiously enough, there are modern forgeries of Marcus Aurelius quotes, trying to mold him in a shape of agnostic or Epicurean materialist.
It is true that contemplative emperor quotes Epicurus rather often, but so does Seneca, with a clever side-note - that he goes to Epicureans as a scout goes to an enemy camp, not to defect, but to gain intelligence.
In all truth there are enough quotes in Marcus Aurelius that mention universal ruling principle and universal mind to put him solidly into camp of at least moderate deists, but there are few curious lines in his Meditations that may put him even further, into the realm of Christians before (revealed) Christ.
Especially if you translate his Greek in the same historical context as (almost contemporary) canonical Gospels.