John Lightfoot on Luke 17:12

[Ten men that were lepers.] I. It is provided by a law, in Leviticus 13:46, that "he that is a leper shall dwell alone, and without the camp." How then came these ten to converse thus together? as also those four together, 2 Kings 7:3?

Other unclean persons must not live with him: i.e. those that are unclean by other kind of defilements: which also is intimated by the Gemarists in these words: "Shall those that have their issues, and those that are defiled by the dead, be sent out into one and the same place? The text saith, 'They shall not defile their camps,' Numbers 5:3; to assign one camp for these, and another for them."

The lepers might be conversant with lepers, and those that had issues with those that had issues; but those that were under different defilements might not converse promiscuously. Which confirms what I have conceived concerning the five porches at the pool of Bethesda; viz., that they were so framed and distinguished at first, that there might be a different reception for those that had contracted different kinds of defilements, and were there waiting to be cleansed in that pool.

That there were certain places where they that were unclean by that disease of the leprosy were secluded, reason might persuade us: for it were an inhuman thing to cast the leprous out of the city without any provision of a dwelling for them, but that they should always lie in the open air. Whether there was any such thing in this place, I will not determine. It seems as if these ten lepers, having heard of our Saviour's coming that way, were got but lately together to attend him there. For when the seventy disciples had beforehand openly proclaimed, in all the places where he was to come, that he would come thither, it is easy to conceive in what infinite throngs the sick, and all that were affected with any kind of distemper, would be crowding thither for a cure.

II. "The leper that transgresseth his bounds, let him receive forty stripes. Those that have their issues, men or women, if they transgress their limits, let them also receive forty stripes." Where the Gloss is, "The limits for those that have their issues are the Mountain of the House, or the Court of the Gentiles: for they are forbid to enter into the camp of the Levites. The unclean are not excluded but from the Court: excepting those that have their issues and a gonorrhea upon them; they are excluded even from the Mountain of the House; and the leper, who is excluded from the camp of Israel, that is, from the city."

Now the camp of Israel, out of which the leper was to be excluded, they interpreted to be every city that had been walled from the days of Joshua: "For (say they) Joshua sanctified the walled cities with the holiness that was ascribed to the camp of Israel; but he did not so to the rest of the land, nor the cities that had no walls." This was a village, and not such a city, where these ten lepers meet our Saviour; and if they were within this village, it was neither beyond the custom nor the rule, provided that they kept but their distance.

"A leper enters into the synagogue: they make him some grates, or bounds, ten hands high and four cubits broad: he enters the first, and goes out the last." The Gloss is, "Lest they should be defiled that stand in the synagogue," &c.