In the show: Arya arrives at The House of Black and White, and is greeted by a familiar face, albeit one thought to be dead: that of Jaqen H'ghar. It is Jaqen we see training Arya to become a Faceless (wo)Man. In the books: Arya is indeed training at the House of Black and White, but under a 'kindly old man' rather than Jaqen. During her training, she is subjected to blindness, has appearance is changed, and she is given assassination assignments. Meanwhile, it is believed that Jaqen has taken on the guise of Pate at the Citadel in Oldtown. What it means: Arya's training is likely to progress in a more-or-less similar fashion, but with Jaqen there as she is more likely to respond to him, and also to give the audience a reference point in a new location. However, with Jaqen supposedly in Oldtown, it does set up the possibility of Arya accompanying him there, and maybe even having a meeting with Sam.