One of the treasures of Thomas’ theology of the Trinity is his attention to the mission of the Spirit, to the gift of the Spirit (and not just to the gifts of the Spirit). In this slightly modified version of the 2016 Aquinas Lecture Oxford, three texts are read that show the richness of his attention to the Spirit and that show, too, that often repeated criticism that Thomas forgets the Spirit is incorrect. First, Thomas’ remark that the knowledge of the divine persons is necessary for a correct understanding of creation and salvation (STh I q. 32, a.1 ad 3m). Second, his commentary on the opening verse of ps 50, (‘the great mercy of God’). Third, two articles on the mission of the Spirit (STh 1, q. 43, a.3 and 5, especially the ad 2m).