The man was obsessed with the PTWP/AA prophecy.
Ironically, though, if R+L does indeed equal J, then all of that misery and bloodshed, tragic as it is, may ultimately be worth it when Jon, along with Dany, Tyrion, and Bran, save everyone from certain annihilation (That is, if GRRM doesn't pull an "UN-PRE-DICTABLE!" on us again.)