A few weeks ago it would've been a very different card! What Luke did to his world, to the people who should have been friends and allies, is not something Gansey can condone. He's also unlikely to fully understand it, though the saving grace is that he's already seen regret in Luke because of it. He thinks that Luke has had his 'Tower' - he's experienced his upheaval, he's crashed down and he's been humbled. He's hoping that it means Luke has a chance to start again - and maybe not start the apocalypse, this time.