Lucretius, answered from the texts and cited to the page.
The whole of it rests on one law: nothing is ever begotten of nothing by divine will. This is the first rule of nature, and it is also the cure for the terror and darkness of the mind, which no sunbeam can scatter, only the outer view and the inner law of nature.1 Men fear because they see things come to pass on earth and in the sky whose causes they cannot discern, and so they suppose a god is working them.
Show them that nothing can arise from nothing, and they will see how each thing is made without the aid of gods. For if things came from nothing, every kind might be born from every other: men from the sea, birds from the sky, with no fixed law of birth, and no need of seed. But the roses come in spring and the corn in summer's heat, each in its season, because fixed seeds bring each thing forth and there dwells in fixed things a power set apart.1
The second half of the law is the same as the first. Nature breaks each thing back into its own first-bodies and does not reduce it to nothing. If anything were mortal in all its parts, it would be snatched from our eyes at once, with no force needed to unloose its fastenings.2 Yet Venus brings back the race of living things into the light of life, earth nurses them, and the rivers keep the sea full.
Infinite time past would long since have devoured all that is of mortal body, so what is renewed must be of immortal nature.2 The rains go down into the lap of earth, our mother; the crops spring up, the cattle fatten, the young sport in the grass, and nature renews one thing from another, nor suffers any birth unless she be requited by another's death.3
So there are first-beginnings, and they are solid and everlasting. If nature had set no limit to the breaking of things, the ages gone by would have ground the bodies of matter so low that nothing could be built from them again, for anything is more easily broken than put together. But we see each thing put together afresh, and fixed seasons ordained for every kind to reach the flower of its life.4
Nor can the first-beginnings be soft, for then there would be no accounting for hard flint and iron.4 They are a close, dense mass of least parts, never compounded from those parts but prevailing in everlasting singleness. If there were no least thing, the half of a half would always have a half, and the tiniest body would be made of infinite parts, no different from the whole sum of things.
Reason cries out against that.5 And the Heraclitean who makes fire alone the substance of all things falls far from true reasoning, since matter that could be dissolved into nothing would lack the diverse fastenings, weights, blows, meetings and movements by which all things are carried on.5 That is the doctrine as I received it from the Greek and put into Latin: seeds and void, a world that makes itself by fixed law, and no god's hand and no terror at its source.
This terror then, this darkness of the mind, must needs be scattered not by the rays of the sun and the gleaming shafts of day, but by the outer view and the inner law of nature; whose first rule shall take its start for us from this, that nothing is ever begotten of nothing by divine will.On the Nature of Things, pp. 32–33
nature breaks up each thing again into its own first-bodies, nor does she destroy anything into nothing.On the Nature of Things, pp. 34–35
Not utterly then perish all things that are seen, since nature renews one thing from out another, nor suffers anything to be begotten, unless she be requited by another's death.On the Nature of Things, pp. 35–36
a set limit to breaking has, we may be sure, been appointed, since we see each thing put together again, and at the same time fixed seasons ordained for all things after their kindOn the Nature of Things, pp. 45–46
The first-beginnings then are of solid singleness; for they are a close dense mass of least parts, never put together out of a union of those parts, but rather prevailing in everlasting singlenessOn the Nature of Things, pp. 47–48