"Go home to thy friends and tell them how great things the Lord hath done for thee" (Mark 5:19). The Lord had shown great mercy to this poor sinner, setting him free from demons and from sin. Now He tells him to go home to his family and friends and be The Lord’s Witness.
Do not go home and begin to preach. Do not go home and take up the great doctrines of grace and expound them. Do not go home and strive to bring everyone to your views and beliefs. Do not go home and condemn all who do not see what you see. Go home and tell them what great things the Lord has done for you! Not what great things you have read or heard, but what great things you have experienced! This is the way to begin our witnessing.
There never is a more interesting story than the story a person has experienced, lived, and felt. If you would really interest others and get their attention, tell them what great things the Lord has done in you and for you!
Notice, the Lord said, "Tell them what great things the Lord hath done." It is a story of free grace. Not what we did, willed, or gave, but what He did for us by his own free, sovereign, and undeserved love. We will not convince them nor change them, any more than another man could convert us. But the Lord, who did great things for us, can do great things for them if He is so pleased. And He is pleased to use the faithful witness of those who go and tell "how great things the Lord hath done for thee."