Lucretius's Epicurean philosophy doesn't deny gods' existence, only that they affect us. Instead, we must aim to be as them
Lucretius follows a materialist philosophy that denies any purpose to the creation of the universe or humanity and asserts that the soul is mortal and there is no afterlife. It doesn't take a great leap of imagination to deduce that the author of De Rerum Natura was not going to be the most popular Latin poet after Constantine's conversion to Christianity. One of the few biographical snippets we have of Lucretius, written by St Jerome, claims that he drank a love potion, went mad, wrote his poem in intervals of lucidity and then killed himself. Although less than 100 years ago some scholars were still attributing aspects of the poem to Lucretius's philtre-induced insanity, it's now generally agreed that Jerome's story is an invention designed to discredit the poet and his philosophy. But Lucretius is not, at least on paper, an atheist, nor is Epicureanism an atheist philosophy. De Rerum Natura discusses the gods, their nature and their relationship with us on more than one occasion, offering us a decent glimpse of Epicurean theology.
In the Epicurean universe, there undoubtedly are gods. Humans perceive the gods – they receive images of them – and those perceptions are true. They do not, however, indulge in any of the bed-hopping, hissy fit-throwing and meddling in human affairs that characterise the gods in Homer or Greek tragedy. The images we receive are of beautiful and untroubled creatures, a model of the repose that Epicurean humans are aiming for. However, our minds often leap from a perception that is true to an opinion that is false, and that happened in the case of the gods: trying to explain earthquakes, thunderbolts and the like, early humans decided that the extraordinary and beautiful gods whose images they received must be the ones shaking the Earth or rending the sky.
The reality couldn't be further removed. Lucretius informs us in no uncertain tones that intrinsic to the very nature of the gods is a complete lack of interest in human affairs. They exist in places utterly unlike our own world (Epicureans believed they lived in the gaps between worlds, with access to unending streams of atoms to replenish their bodies, which enables them to be immortal); they are perceptible only mentally, and are completely intangible (Lucretius promises in book five to explain their physical make-up in greater detail, but that explanation seems never to have been written). Remote from and unlike us, they have no need of us: our offerings, prayers and gratitude are completely irrelevant to them. As for the thunderbolts and earthquakes, they are of course, among the many natural physical phenomena for which Lucretius gives a host of explanations in his fifth and sixth books; none of those explanations, of course, involve the gods.
Lucretius is, on occasion, less than flattering about some aspects of religious ritual: there is a tour de force condemnation of the sacrifice of Iphigenia in book one, and a cameo appearance by a mother cow whose calf has been bloodily sacrificed in book two. But Epicureans did participate in religious practice. The aim, as Lucretius expresses in book 6, was to do so with the untroubled, fearless heart that is the product of understanding the gods' nature in the first place. We are also allowed to talk about gods metonymically or allegorically, calling wine Bacchus or the earth the mother of the gods, provided we remember that this is simply imagery and implies nothing true about the universe.
That is handy for Lucretius, as, being an epic poet, he mentions the gods on more than one occasion: indeed, the reason he clarifies that we can use phrases such as "mother of the gods" is that he has just spent a good few lines describing the rituals of the earth mother goddess, Magna Mater, with allegorical details that he himself makes clear are all false. The poem opens with a picture of Venus, the goddess mother of Aeneas, as the force underlying all creation – genetrix is the Latin word used – asking her to be Lucretius's ally as he writes. That passage has caused much scholarly head-scratching, but the solution to it seems to lie in the warning Lucretius gives us after Magna Mater. Say these things by all means, if you understand why they aren't true – which, of course, Lucretius does, and we too will by the time we have finished reading his poem, and have learnt that atoms are what actually generate everything (Lucretius often calls them genitalia corpora), and that the Venus called genetrix at the poem's start is a poetic licence. The conventional gods who strike so much fear into our hearts are just another weapon in the argumentative arsenal the poet deploys to get us to think and live like the actual gods.