The Jedi leader Nellith whom Obi-Wan interacts with in Episode II was a struggle to figure out for a long time before I recently I finally put it together who she is.
Nellith is the retired gunslinger/samurai, a former Knight who's embraced a new life as a teacher and philosopher similar to how many have in the past few centuries since more of them have moved away from being Knights. She's the embodiment of what the Jedi have been allowed to become, choosing to spread throughout the galaxy and help individuals rather than being a military force at the behest of an increasingly corrupt Senate.
Her conflict with Kenobi is one of irony, with the centuries old Nellith (the oldest student of Yoda still living) representing the new Jedi and the young Obi-Wan lobbying for a return to what the Jedi used to be in order win the Clone Wars. The nature of this change, turning whole generations of Jedi engineers, farmers, and healers into Knights on the frontline is at the heart of the divide between them.
To him the logic is simple, have Jedi pick up the lightsaber again, defend the Republic when it needs it the most, and when the peace is won, return of their old lives. Nellith is old warrior though, and knows it won't be that simple. This war will change them, and therein lies a risk greater than their Mandalorian foes because with this war lies the risk of Jedi turning to the dark side, something she knows all too well.
Indeed, while Nellith is the obvious parallel to Kenobi (a student of Yoda now acting as a leader) she also parallels Anakin, being a Jedi who almost fell to the dark side herself many years before, and just barely being able to pull herself back. Her history and her revelation of how she defeated that temptation foreshadows what Anakin will eventually not be able to do in his greatest moment of seduction by the dark side.
That moment in her past colors all of her actions in episode II and III; why she chose to put down her lightsaber, why she fears the emotional dark side temptation will face in the war if they go to the front lines, and why she senses that the Jedi will not be the same when the war is over.