Mark 5:20

And he departed, and began to publish in Decapolis
He submitted to the will of Christ, though he could gladly have gone with him; he hearkened to his instructions, took his advice, and obeyed his commands, as every one that has received favours from him ought to do and he went not only to his own, or his father's house, and acquainted his nearest friends and relations with what had befallen him, but he published the account, as Luke says, ( Luke 8:39 ) , throughout the whole city, very likely of Gadara, where he might be a native; and which, as Pliny ^F12 relates, was in Decapolis, and agrees with the accounts of both the evangelists: here he published, as Christ had ordered him,

how great things Jesus had done for him:
only instead of saying the Lord had done them, for him, he attributed them to Jesus, who: is Lord and God; and by that miracle, as by many others, gave full proof of his deity, as well, as Messiahship. This is an instance of the obedience of faith, and is a considerable branch of it; for, as with the heart, men believe in Christ unto righteousness, so, with the mouth, confession must be made to the glory of that salvation which Christ has wrought out: many are backward to this part of the service of faith, through fears, through unbelief, and Satan's temptations; but this man, though to have continued with Christ was greatly desirable by him, yet he submits to his will and pleasure, and is obedient to his orders; and that at once, immediately dropping his suit: unto him, no longer insisting on his being with him; for he was sensible of the great obligations he was laid under to him, and saw it to be his duty to observe whatever he commanded him: and this was indeed but a reasonable, piece of service, and what if he had not been ordered to do, one would think he could not have done otherwise; at least, had he not, he would not have acted the grateful and generous part: and indeed, if such for whom the Lord has done great things as these, should hold their peace, the stones would even cry out.

And all men did marvel;
at the power of Jesus, at the miracle wrought by him, and the benefit the man had received, who they all knew had been in so deplorable a condition. It is not only marvellous to the persons themselves, for whom great things are done by the Lord; but it is amazing to others, to angels and men, when it is considered who they are, on whose account they are wrought; great sinners, very unworthy of such high favours, yea, deserving of the wrath of God, and of eternal damnation; and likewise, who it is that has done these things for them, the Lord of heaven and earth; he against whom they have sinned, and is able both to save, and to destroy; he who is the great God, is their Saviour; to which may be added, the consequence of these things, they issue in everlasting glory and happiness.