A.T. Robertson Commentary Mark 5:20

"And he went his way, and began to publish in Decapolis how great things Jesus had done for him: and all men marvelled." — Mark 5:20 (ASV)

He went his way (απηλθεν). He went off and did as Jesus told him. He heralded (κηρυσσειν) or published the story till all over Decapolis men marvelled (εθαυμαζον) at what Jesus did, kept on marvelling (imperfect tense). The man had a greater opportunity for Christ right in his home land than anywhere else. They all knew this once wild demoniac who now was a new man in Christ Jesus. Thousands of like cases of conversion under Christ's power have happened in rescue missions in our cities.