2 The Lord came: what did He do? He set forth a great mystery. “He spat on the ground,” He made clay of His spittle; for the Word was made flesh. “And He anointed the eyes of the blind man.” The anointing had taken place, and yet he saw not. He sent him to the pool which is called Siloam. But it was the evangelist's concern to call our attention to the name of this pool; and he adds, “Which is interpreted, Sent.” You understand now who it is that was sent; for had He not been sent, none of us would have been set free from iniquity.
Accordingly he washed his eyes in that pool which is interpreted, Sent— he was baptized in Christ. If, therefore, when He baptized him in a manner in Himself, He then enlightened him; when He anointed Him, perhaps He made him a catechumen. In many different ways indeed may the profound meaning of such a sacramental act be set forth and handled; but let this suffice your Charity. You have heard a great mystery. Ask a man, Are you a Christian? His answer to you is, I am not, if he is a pagan or a Jew.
But if he says, I am; you inquire again of him, Are you a catechumen or a believer? If he reply, A catechumen; he has been anointed, but not yet washed. But how anointed? Inquire, and he will answer you. Inquire of him in whom he believes. In that very respect in which he is a catechumen he says, In Christ. See, I am speaking in a way both to the faithful and to catechumens. What have I said of the spittle and the clay? That the Word was made flesh. This even catechumens hear; but that to which they have been anointed is not all they need; let them hasten to the font if they are in search of enlightenment.
Source: Tractates on the Gospel of John (New Advent)