He says not, “the work of the Spirit,” but, “the fruit of the Spirit.” Is the soul, however, superfluous? The flesh and the Spirit are mentioned, but where is the soul? Is he discoursing of beings without a soul? For if the things of the flesh be evil, and those of the Spirit good, the soul must be superfluous. By no means, for the mastery of the passions belongs to her, and concerns her; and being placed amid vice and virtue, if she has used the body fitly, she has wrought it to be spiritual, but if she separate from the Spirit and give herself up to evil desires, she makes herself more earthly. You observe throughout that his discourse does not relate to the substance of the flesh, but to the moral choice, which is or is not vicious. And why does he say, “the fruit of the Spirit?” it is because evil works originate in ourselves alone, and therefore he calls them “works,” but good works require not only our diligence but God's loving kindness. He places first the root of these good things, and then proceeds to recount them, in these words, “Love, joy, peace, long-suffering, kindness, goodness, faithfulness, meekness, temperance; against such there is no law.” For who would lay any command on him who has all things within himself, and who has love for the finished mistress of philosophy? As horses, who are docile and do every thing of their own accord, need not the lash, so neither does the soul, which by the Spirit has attained to excellence, need the admonitions of the Law. Here too he completely and strikingly casts out the Law, not as bad, but as inferior to the philosophy given by the Spirit.
Ver. 24. “And they that are of Christ Jesus have crucified the flesh with the passions and the lusts thereof.”
That they might not object, “And who is such a man as this?” he points out by their works those who have attained to this perfection, here again giving the name of the “flesh” to evil actions. He does not mean that they had destroyed their flesh, otherwise how were they going to live? For that which is crucified is dead and inoperative, but he indicates the perfect rule of life. For the desires, although they are troublesome, rage in vain. Since then such is the power of the Spirit, let us live therein and be content therewith, as he adds himself,
Ver. 25. “If we live by the Spirit, by the Spirit let us also walk,”
— being governed by His laws. For this is the force of the words “let us walk,” that is, let us be content with the power of the Spirit, and seek no help from the Law. Then, signifying that those who would fain have introduced circumcision were actuated by ambitious motives, he says,
Ver. 26. “Let us not be vainglorious,” which is the cause of all evils, “provoking one another” to contentions and strife, “envying one another,” for from vainglory comes envy and from envy all these countless evils.
Source: Commentary on Galatians (New Advent)