You know as well as I that one cannot command the feelings of another to be as we wish. Yet Jesus does that here. He commands his disciples not to let their hearts be troubled. Ahead of the disciples was a time of change, and trouble. We no doubt will face changes, hopefully not trouble.
Heart trouble is the most common thing in the world.
No rank, or class, or condition is exempt from it. No bars, or bolts, or locks can keep it out. Even the best of Christians have many bitter cups to drink between grace and glory. Even the holiest of saints find the world a vale of tears. Jesus had a remedy for trouble in this passage.