Before sacrifice, the lexicographer Julius Pollux tells us, one must be cleansed or purified. He does not tell us exactly how this works, but he gives us a survey of the vocabulary connected to purification (and impurity), which is translated below.
Sometimes, purification could involve a complex ritual. But as another passage in Pollux and a scholium from Proclus indicate, the principal requirement was to be clean and use clean things, and to act with a pure mind. Proclus, and a temple inscription at Epidaurus, even tell us that the right mental or moral attitude is the principal aspect of purity.
Mental state set aside, the most important act of purification was washing your hands, which is sufficient for prayer and private offerings (as long as one is washed and wearing clean clothes). Despite persistent rumors, one does not need a specially prepared “lustral water” or khernips for this; khernips is simply any hand-washing water. Beyond this, there are, according to Servius, three kinds of purification in all, not just by water, but also by fire and by air.
1 The Epidaurian Inscription (from Porphyry, On Abstinence 2.19)
The one who goes into the temple that is fragrant with incense (thyōdēs) must be pure (hagnós); and purity is thinking holy thoughts (phronein hosia).
1 Translation (Julius Pollux, Onomasticon 1.32–33)
Before the sacrifices (hiera), there are sprinklings (perirrhantēria) and purifications (katharmoi, katharseis) purificatory items (katharsia, kathartēria), purifiers (kathartai).
Those who have made use of these are pure (katharoi), whose opposite are the impure (akathartoi). The former are present in a pure manner (katharōs), in a holy manner (hosio-), in a hallowed manner (hagn-, hagi-); the unholy (anosioi, anieroi), do all things in a manner not hallowed, not holy, not pure, polluted, entirely polluted, impure, involved in guilt, caught in pollution.
And their actions (? pragmata) are, on the one hand, the hallowed (hagion), pure (katharon), holy (hosion), hallowed (hagnon), pure (euages), immaculate (akhranton), and on the other, the impure (enages), unhallowed (exagiston), impure (dysages), polluted, entirely polluted, pollution (miasma), defilement (mysos).
By a different usage, (we can say) to be purified, for pollution to be purged, for impurity (agos) to be gotten rid of, for defilement to be dissolved (ly-), averted (apotrepsasthai), banished.
4 From Pollux’ discussion of sacrifice
One must approach the gods purified, cleansed, besprinkled, washed, clean, hallowed, sanctified; with a pure mind; with newly made garments or with freshly washed clothes.
5 From Proclus’ commentary on Hesiod, Works and Days 336
Those who wish to undertake sacrificial operations must principally pursue pure rectitude, both in their way of life and also in all sacred instruments, the places in which offerings are to be made, and the ornaments on our bodies. The former (=our life) must be contrary to all licentiousness, all injustice, all passion; and we may say that we must purify our way of life first, and only then observe the offering of foods and drinks according to ancestral custom; seeing that for different people, there are different customs by which someone who takes part in traditional sacrifices is restricted. For it is ridiculous if people who use the purest things in their offerings make use of anything impure, whether they do this only in their defiled houses or offer a portion gotten from some polluted activity in their sacrifice, or whether they wear unclean clothes, just as we are told that we should not use use fire from an unpurified house as the fire for purifying everything else.