More on the Wikipedia entry for asha. It would seem it functions in very much the capacity of 'Logos' in Greek i.e. that which governs the universe:
Subject to context, aša/arta- is also frequently translated as "right working" or "[that which is] right". The word then (cf. Bartholomae's[16] and Geldner's[17] translations as German language "Recht") has the same range of meaning of "right" as in the English language: truth, righteousness, rightfulness, lawfullness, conformity, accord, order (cosmic order, social order, moral order).
These various meanings of "right" are frequently combined, such as "the inexorable law of righteousness,"[18] or as "the eternal fitness of things that are in accord with the divine order."[19]
As (the hypostasis of) regularity and "right working", aša/arta- is present when Ahura Mazda fixed the course of the sun, the moon and the stars (Yasna 44.3), and it is through aša that plants grow (Yasna 48.6).
"Right working" also overlaps with both Indo-European *ár- "to (properly) join together" and with the notion of existence and realization (to make real). The word for "established", arəta-, also means "proper". The antonymic anarəta- (or anarəθa-) means "improper[20] In Zoroastrian tradition, prayers must be enunciated with care for them to be effective. The Indo-Iranian formula *sātyas mantras (Yasna 31.6: haiθīm mathrem) "does not simply mean 'true Word' but formulated thought which is in conformity with the reality' or 'poetic (religious) formula with inherent fulfillment (realization)'".[14]
It perhaps has also suggestions of harmoniousness or cooperativeness
And then back to fire (remembering what Philo says about fire being the Logos):
Asha Vahishta is closely associated with fire. Fire is "grandly conceived as a force informing all the other Amesha Spentas, giving them warmth and the spark of life."[25] In Yasht 17.20, Angra Mainyu clamours that Zoroaster burns him with Asha Vahishta. In Vendidad 4.54-55, speaking against the truth and violating the sanctity of promise is detected by the consumption of "water, blazing, of golden color, having the power to detect guilt."
This analogy of truth that burns and detecting truth through fire is already attested in the very earliest texts, that is, in the Gathas and in the Yasna Haptanghaiti. In Yasna 43-44, Ahura Mazda dispenses justice through radiance of His fire and the strength of aša. Fire "detects" sinners "by hand-grasping" (Yasna 34.4). An individual who has passed the fiery test (garmo-varah, ordeal by heat), has attained physical and spiritual strength, wisdom, truth and love with serenity (Yasna 30.7). Altogether, "there are said to have been some 30 kinds of fiery tests in all."[26] According to the post-Sassanid Dadestan i denig (I.31.10), at the final judgement a river of molten metal will cover the earth. The righteous, as they wade through this river, will perceive the molten metal as a bath of warm milk. The wicked will be scorched. For details on aša's role in personal and final judgement, see aša in eschatology, below.
Fire is moreover the "auxiliary of the truth," "and not only, as in the ordeal, of justice and of truth at the same time."[10] In Yasna 31.19, "the man who thinks of aša, [...] who uses his tongue in order to speak correctly, [does so] with the aid of brilliant fire". In Yasna 34-44 devotees "ardently desire [Mazda's] mighty fire, through aša." In Yasna 43-44, Ahura Mazda "shall come to [Zoroaster] through the splendour of [Mazda's] fire, possessing the strength of (through) aša and good mind (=Vohu Manah)." That fire "possesses strength through aša" is repeated again in Yasna 43.4. In Yasna 43.9, Zoroaster, wishing to serve fire, gives his attention to aša. In Yasna 37.1, in a list of what are otherwise all physical creations, aša takes the place of fire.
Asha Vahishta's association with atar is carried forward in the post-Gathic texts, and they are often mentioned together. In Zoroastrian cosmogony, each of the Amesha Spentas represents one aspect of creation and one of seven primordial elements that in Zoroastrian tradition are the basis of that creation. In this matrix, aša/arta is the origin of fire, Avestan atar, which permeates through all Creation. The correspondence then is that aša/arta "penetrates all ethical life, as fire penetrates all physical being."[11]
In the liturgy Asha Vahishta is frequently invoked together with fire. (Yasna l.4, 2.4, 3.6, 4.9, 6.3, 7.6, 17.3, 22.6, 59.3, 62.3 etc.). In one passage, fire is a protector of aša: "when the Evil Spirit assailed the creation of Good Truth, Good Thought and Fire intervened" (Yasht 13.77)
In later Zoroastrian tradition, Asha Vahishta is still at times identified with the fire of the household hearth.[27]
In eschatology and soteriology[edit]
In addition to the role of fire as the agent of Truth, fire, among its various other manifestations, is also "the fire of judicial ordeal, prototype of the fiery torrent of judgement day, when all will receive their just deserts 'by fire and by Aša' (Y 31.3)."[25]
In the Avesta, the "radiant quarters" of aša is "the best existence", i.e. Paradise (cf. Vendidad 19.36), entry to which is restricted to those who are recognized as "possessing truth" (ašavan).[28] The key to this doctrine is Yasna 16.7: "We worship the radiant quarters of Aša in which dwell the souls of the dead, the Fravašis of the ašavans; the best existence (=Paradise) of the ašavans we worship, (which is) light and according all comforts."[28]
'Aša' derives from the same Proto-Indo-European root as 'Airyaman', the divinity of healing who is closely associated with Asha Vahishta. At the last judgement, the common noun airyaman is an epithet of the saoshyans, the saviours that bring about the final renovation of the world. The standing epithet of these saviour figures is 'astvatәrәta', which likewise has arta as an element of the name.[20] These saviours are those who follow Ahura Mazda's teaching "with acts inspired by aša" (Yasna 48.12). Both Airyaman and Asha Vahishta (as also Atar) are closely associated with Sraosha "[Voice of] Conscience" and guardian of the Chinvat bridge across which souls must pass.
According to a lost Avestan passage that is only preserved in a later (9th century) Pahlavi text, towards the end of time and the final renovation, Aša and Airyaman will together come upon the earth to do battle with the Az, the demon of greed (Zatspram 34.38-39).
The third Yasht, which is nominally addressed to Asha Vahishta, is in fact mostly devoted to the praise of the airyaman ishya (airyәmā īšyo, "Longed-for airyaman"), the fourth of the four great Gathic prayers. In present-day Zoroastrianism it is considered to invoke Airyaman just as the Ashem Vohu, is the second of the four great Gathic prayers, is dedicated to Aša. All four prayers (the first is the Ahuna Vairya, the third is the Yenghe Hatam) have judgement and/or salvation as a theme, and all four call on the Truth.
It is Airyaman that – together with fire – will "melt the metal in the hills and mountains, and it will be upon the earth like a river" (Bundahishn 34.18). In Zoroastrian tradition, metal is the domain of Xshathra [Vairya], the Amesha Spenta of "[Desirable] Dominion", with whom Aša is again frequently identified. Dominion is moreover "a form of truth and results from truth."[29]
In Denkard 8.37.13, Asha Vahishta actually takes over Airyaman's healer role as the healer of all spiritual ills and Airyaman then only retains the role of healer of corporeal ills. Although Airyaman has no dedication in the Siroza, the invocations to the divinities of the Zoroastrian calendar, Airyaman is twice invoked together with Aša. (Siroza 1.3 and 2.3)
Aogemadaecha 41-47 prototypes death as a journey that has to be properly prepared for: As mortals acquires material goods as they go through life, so also should they furnish themselves with spiritual stores of righteousness. They will then be well provisioned when they embark on the journey from which they will not return.
Aša's role is not limited to judgement: In Bundahishn 26.35, Aša prevents demons from exacting too great a punishment to souls consigned to hell. Here, Aša occupies the position that other texts assign to Mithra, who is traditionally identified with fairness.
For the relationship between Aša, eschatology and Nowruz, see in the Zoroastrian calendar, below.
Although there are numerous eschatological parallels between Aša and Aši "recompense, reward" (most notably their respective associations with Sraosha and Vohu Manah), and are on occasion even mentioned together (Yasna 51.10), the two are not etymologically related. The feminine abstract noun aši/arti derives from ar-, "to allot, to grant." Aši also has no Vedic equivalent.