Moses indicates figuratively that the soul should not be divided in will between good and evil, but should pursue the good alone; and that it must cultivate not the dual fruits of virtue and vice but those of virtue only. For he says: “Do not yoke together on your threshing floor animals of a different species, such as ox and ass; but yoke together animals of the same species and so thresh your corn” (Deuteronomy 22:10). This is to say, do not let virtue and vice work together on the threshing floor of your heart, but let virtue alone work there.
Again he says: “Do not weave flax into a woolen garment, or wool into a linen garment” (Deut. 22:11); and: “Do not cultivate two kinds of fruit together on the same patch of your land” (Deut. 22:9)….All this is a concealed way of saying that you must not cultivate virtue and vice together in yourself, but you must devote yourself singlemindedly to producing the fruits of virtue; and you must not share your soul with two spirits–the Spirit of God and the spirit of the world–but you must give it solely to the Spirit of God and must reap only the fruits of the Spirit.
~St Makarios of Egypt (paraphrased by St Symeon Metaphrastis)