Jordan’s reflections on “leprosy” help to explain why Miriam, and not Aaron, becomes leprous in Numbers 12.

Jordan notes that the term for “plague” used in Leviticus 13 is actually “touch,” and suggests that the leper is “touched” by Yahweh, sometimes in response to sacrilege, a violation of God’s holiness. Touch Yahweh’s stuff; Yahweh touches you.

This touch communicates holiness, in part or in whole. When the “leper” becomes completely covered with white skin, he is pronounced clean; he is wholly holy, and is able to function in the sanctuary without fear. In other words, the complete “leper” is analogous to the high priest, clothed in skin of glorious white.

Now apply this to Numbers 12: Aaron is already holy, already touched by Yahweh. He and Miriam both lay a finger on Yahweh’s designated leader. But Aaron is already “white” with priestly garments; so only Miriam is touched with leprosy.