The Saviour willed to be baptized not that He might Himself be cleansed, but to cleanse the water for us. [ed. note: This is the doctrine of S. Austin, in Joan. iv. 14. Op. Imp. contr. Julian iv. 63. Ambros. in Luke ii, 83, &c. &c. vid. Pusey on Baptism, p. 279. ed. 2]
From the time that Himself was dipped in the water, from that time has He washed away all our sins in water. And let none wonder that water, itself corporeal substance, is said to be effectual to the purification of the soul; it is so effectual, reaching to and searching out the hidden recesses of the conscience. Subtle and penetrating in its own nature, made yet more so by Christ’s blessing, it touches the hidden springs of life, the secret places of the soul, by virtue of its all-pervading dew. The course of blessing is even yet more penetrating than the flow of waters. Thus the blessing which like a spiritual river flows on from the Saviour’s baptism, hath filled the basins of all pools, and the courses of all fountains.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: non occ., cf. Ambrosiaster, Serm. 12. 4