Albert Barnes on Luke 17:12

There met him. They were in his way, or in his path, as he was entering the village. They were not allowed to enter the village while they were afflicted with the leprosy, Lev 13:46, Nu 5:2,3

Lepers. Mt 8:2.

Stood afar off. At a distance, as they were required by law. They were unclean, and it was not lawful for them to come near to those who were in health. As Jesus was travelling, they were also walking in the contrary way, and seeing him, and knowing that they were unclean, they stopped or turned aside, so that they might not expose others to the contagion.

(h) "stood afar off" Lev 13:46