And because this faculty cannot be realised in act in its entirety at one time by a single man, nor by any of the individual societies which we have marked, therefore there must be multitude in the human race, in order to realise it: just as it is necessary that there should be a multitude of things which can be brought into being,[156] so that the capacity of the primal matter for being acted on may be ever open to what acts on it. For if this were not so, we could speak of a capacity apart from its substance, which is impossible. And with this opinion Averroes, in his comment on [Aristotle's] treatise on the Soul, agrees. For the capacity for understanding, of which I speak, is concerned not only with universal forms or species, but also, by a kind of extension, with particular ones. Therefore it is commonly said that the speculative understanding becomes practical by extension; and then its end is to do and to make. This I say in reference to things which may be _done_, which are regulated by political wisdom, and in reference to things which may be _made_, which are regulated by art; all which things wait as handmaidens on the speculative intellect, as on that best good, for which the Primal Goodness created the human race. Hence the saying of the Politics[157] that those who are strong in understanding are the natural rulers of others. [Footnote 156: "_Generabilium._"] [Footnote 157: Arist. _Polit._ i. 5, 6.--(W.)] IV.--It has thus been sufficiently set forth that the proper work of the human race, taken as a whole, is to set in action the whole capacity of that understanding which is capable of development: first in the way of speculation, and then, by its extension, in the way of action. And seeing that what is true of a part is true also of the whole, and that it is by rest and quiet that the individual man becomes perfect in wisdom and prudence; so the human race, by living in the calm and tranquillity of peace, applies itself most freely and easily to its proper work; a work which, according to the saying; "Thou hast made him a little lower than the angels," is almost divine. Whence it is manifest that of all things that are ordered to secure blessings to men, peace is the best. And hence the word which sounded to the shepherds from above was not riches, nor pleasure, nor honour, nor length of life, nor health, nor strength, nor beauty; but peace. For the heavenly host said: "Glory to God in the highest, and on earth, peace to men of goodwill." Therefore also, "Peace be with you," was the salutation of the Saviour of mankind. For it behoved Him, who was the greatest of saviours, to utter in His greeting the greatest of saving blessings. And this custom His disciples too chose to preserve; and Paul also did the same in his greetings, as may appear manifest to all.