Killian giving Emma the advice to live in the here and now after someone you loved has died, is a very important sign of character growth. Killian has lived in the past for over 300 year before he finally was able to move on. His constant drive for revenge, both on the King as well as on Rumpelstiltskin, were fed by his constant reminders of their deaths: the Jolly Roger and his hook. He relived their deaths every day he spent on his ship and every moment he looked at his hook. He doesn’t want Emma to experience the same darkness that he has faced, the darkness that made him first Captain Jones and then Captain Hook. He’s Killian again, regretting his past and, most importantly, trying to save Emma’s soul.