Note the word potuit, used here as well as in Lucretius: Tantum potuit religio suadere malorum. "So potent was religion in persuading to evil deeds."
So that the power or ability to know the causes of things--a power given by philosophy--is balanced against the power we give to superstition through fear and ignorance. The power of knowledge allows us to trample fear, fate, and the dread of death.
It is the gift of Epicurus to the world, as Lucian indicates:
"The fellow had no conception of the blessings conferred by that book upon its readers, of the peace, tranquillity, and independence of mind it produces, of the protection it gives against terrors, phantoms, and marvels, vain hopes and inordinate desires, of the judgement and candour that it fosters, or of its true purging of the spirit, not with torches and squills and such rubbish, but with right reason, truth, and frankness."
Thoreau saw the figure of Epicurus in Lucretius as a kind of Prometheus, stealing fire from the gods and giving it to man.