The only admissible
meaning, therefore, is: “By purifying it by the baptism of water (instrumental
dative) by means of a word” (εν instrumental).—The baptismal water alone has
not the power to purify the soul; there must be added to it “a word,” which is indeed
the formula of baptism, although it is designated here only generically . . . (Fernand
Prat, The Theology of Saint Paul, 2 vols. [trans. John L. Stoddard;
Westminster, Md.: The Newman Bookshop, 1927], 2:256 n. 2)