Much of the appeal of Eiichiro Oda's One Piece comes from the awesome action, crazy ideas, and goofy humor, but the core of the series is the characters and their relationships, fitting into the shonen manga template of friendship and loyalty. The Water Seven arc has seen the bond between our heroes shaken a bit, with the apparent betrayal of the crew by Nico Robin hitting them especially hard. So when we learn her true motives in volume 38, Nami's reaction to the news perfectly sums up the catharsis that both she and the reader feels:
That last line is key; the power of friendship is what gives these characters their strength, and the relief that they feel when they learn that their loyalty wasn't misplaced is enough to provide strength to overcome any obstacles. Victory by our heroes is pretty much always assured, but by providing such heartfelt motivation, Oda keeps the struggles from being formulaic and obvious. I can't wait to see how they use this strength to win over the impossible odds this time.