Jesus insisted that the former demoniac stay with his own people. They would not listen to Jesus directly, but this man could be an ambassador for the Lord. They might be less afraid with him as a mediator, and so become open to the life Christ offered to them with a little bit of distance between themselves and the power of His words.
We are also called to be His ambassadors to people afraid to interact with Him directly. We will be more effective if we recognize and remember the immense power He holds and can share personal experiences we have had with the Lord of life. Part of the reason He doesn't show His power as directly with everyone in the world as He did with this one demoniac is because it is so overwhelming for so many. Yet we know it's reality and we can share it through our testimonies so that others can receive life in Him despite their fear.