“As Jesus was getting into the boat, the man who had been demon-possessed begged to go with him”. 
Mk 5:18 NIV 

It is told that once, in the days before the ending of slavery, Lincoln bought a slave girl with the sole purpose of giving her her freedom. She did not realize why he was buying her; she thought it was just another transaction in which she was involved as a thing. So he paid the price for her; and then he handed her papers of freedom to her. She did not even understand. ‘You are free’, he said to her gently. ‘Free?’ she said. ‘Can I go wherever I want to go now?’ ‘Indeed you can’ he said. ‘Then’ she said, ‘if I am free to go anywhere I will stay with you and serve you until I die’. Legally she was free; but love and gratitude had bound her in a new and willing service (W. Barclay, The Plain Man Looks at the Apostles’ Creed, p67). 
The man who had been possessed by the legion of demons was overwhelmed by what Jesus had done for him. In contrast to the other residents of the region of the Gerasenes he wanted to be with Jesus and to become one of his disciples. Gratitude for his release from bondage to those evil spirits prompted him to want to be with Jesus and to serve him. 
Christian disciples have seen what Jesus did for them on the cross and how he sacrificed his life for them. Dwelling long and deeply on that personal event they well up with thanksgiving to Christ and offer themselves in some form of service or ministry. And worship becomes for them a “sacrifice of praise and thanksgiving”. 

Lord, let my whole life be a hymn of thanks to you.