With the resurrection, Jesus is ending the time where he walks among his disciples to empower them to make new disciples. It's quite an act of faith on his part. These people he has spend only a few years teaching are now entrusted with carrying on the things which they probably barely understand themselves. What makes it possible? They're not doing it on their own, even when they're not sharing the dusty roads with him. He is with them always, and is with us as well.