10 “And there came a woman.” Figure of the Church not yet justified, but now about to be justified: for this is the subject of the discourse. She comes ignorant, she finds Him, and there is a dealing with her. Let us see what, and wherefore. “There comes a woman of Samaria to draw water.” The Samaritans did not belong to the nation of the Jews: they were foreigners, though they inhabited neighboring lands. It would take a long time to relate the origin of the Samaritans; that we may not be detained by long discourse of this, and leave necessary matters unsaid, suffice to say, then, that we regard the Samaritans as aliens.
And, lest you should think that I have said this with more boldness than truth, hear the Lord Jesus Himself, what He said of that Samaritan, one of the ten lepers whom He had cleansed, who alone returned to give thanks: “Were there not ten cleansed? And where are the nine? There was not another to give glory to God, save this stranger.” It is pertinent to the image of the reality, that this woman, who bore the type of the Church, comes of strangers: for the Church was to come of the Gentiles, an alien from the race of the Jews.
In that woman, then, let us hear ourselves, and in her acknowledge ourselves, and in her give thanks to God for ourselves. For she was the figure, not the reality; for she both first showed forth the figure and became the reality. For she believed on Him who, of her, set the figure before us. “She comes, then, to draw water.” Had simply come to draw water, as people are wont to do, be they men or women.
Source: Tractates on the Gospel of John (New Advent)