Your goal is to get every one of them to climb to the top of Everest.
A rare few have so much faith in you that telling them you're going to help them be able to climb to the top of the world will be all the motivation they need.
But for most of them, if you tell them what your ultimate goal is for them, you'll fail before you even start. Just get them to the top of a hill. Then a higher hill. Then climb to the ridge of a lower peak. Before they know it, they will appreciate your companionship more than enough to compensate for the fatigue and hardship. Once you leave, they will go on to scale higher and higher peaks, just for the thrill of becoming like you, and remembering what it was like to climb with you. And the ones who don't make it to Everest you will find either at the summits of other mountains or else helping others to climb just as you helped them.