This argument is confidently urged by St Ambrose, De Spiritu Sancto, ii, 6, from whom St Thomas takes it. The value of it depends on a variant reading in the Greek. The textus receptus has hoi pneumati theô latreuontes; and such must have been the reading of St Chrysostom, who explains pneumati, toutestin, pneumatikôs: with this interpretation, he cannot have read theou, as MSS represent him. The Vulgate agrees, qui spiritu Deo servimus, 'we who in spirit serve the Lord.' So too à Lapide. with this reading, theô, which St Thomas also supposes, the interpretation which he gives cannot stand. We who serve the Spirit of God, would require hoi theô tô pneumati latreuontes. For the text as it stands, 'we who serve God as a Spirit,' is quite a possible translation (cf. John iv, 24), though that is not to St Thomas's purpose. But there is another reading, theou, adopted by Westcott and Hort. St Thomas was a stranger to this reading, but it is the making of his argument. hoi pneumati theou latreuontes can only mean 'we who serve the Spirit of God.' I am inclined, however, to think that the Vulgate is right, that theô is the reading, that pneumati means pneumatikôs and that the argument is untenable.
Of God and His Creatures: 4.17