"Thomas was not original in speaking of the Holy Spirit as the soul of the mystical Body. But he was alone in his epoque (Martin Grabmann, Die Lehre des heiligen Thomas von Aquin von der Kirche als Gotteswerk: ihre Stellung im thomistischen System und in der Geschichte der mittelalterlichen Theologie (Regensburg: G. J. Manz, 1903), pp.. 184-193) in making him [(lui)] play the role of 'heart of the Church' (Summa theol. III.8.1.ad 3; De ver. 29.4.ad 7): if, in the Church-body to be head is fitting for Christ, for he has manifested himself in a very visible fashion, the role of heart falls back on the Holy Spirit. 'It is the heart, that is to say love, that is the supreme cause of the life and unity of the Church' (Journet). Th[at] metaphor calls for another: charity comes from the Holy Spirit, as blood from the heart; binding all of the members to one another, [charity (elle)] makes [it so] that the meritorious works of each profit all of the others. The Holy Spirit is the heart of the communion of the saints (Jean-Pierre Torrrell, "La pratique pastorale d'un théologien du XIIIe siècle: Thomas d'Aquin prédicateur," Revue thomiste 82 (1982): 237-240 (213-245))".
Jean-Pierre Torrell, “Thomas d’Aquin,” Dictionnaire de spiritualité 15 (1991), col. 761 (718-773). As for the masculine language, though "lui" is both masculine and feminine, Torrell uses "le" for the Holy Spirit throughout this article.