Whether the Essence of Goodness Consists in Mode, Species and Order?
What Aquinas is saying here (ST, I, 5, 5), it seems to me, is that the essence of goodness in any piece of art, whether divine or human, consists in the proper application of the four causes to fashion it. Thus, the right materials (material cause) and the proper employment of the power of the artist (efficient cause) constitute “mode.” “The form itself [formal cause] is signified by the species; for everything is placed in its species by its form.” And the purpose, the part that the thing plays in the overall scheme of things, that is, the final cause, for the sake of which the form was given to matter and towards which it now “acts and tends” in accordance with the nature of the form, makes up “order”.
And that makes sense, for if any one of causes is not correctly applied by the artist to his creation, the creation will not be perfect.