On the OPC email discussion list, Dean asked,

In Mark 5:19 Jesus says, "Go home to your friends, and tell them what great things the Lord has done for you, and how He has had compassion on you." The man returns to Decapolis, but toward the end of Mark 7 when Jesus visits Decapolis and performs a miracle "He commanded them that they should tell no one."

Why the two different instructions from Jesus for the same geographic region?

Many Reformed commentaries (see John Calvin, Matthew Henry) give the following good explanation of the several places where Jesus told people not to tell anyone about Him and His works, which is also known as the "Messianic secret":  it was not yet the time for Christ to be delivered over to the hands of sinful men to be crucified, and then to be raised from the dead and exalted to the right hand of God the Father.  But there was a turning point when Christ said "The hour has come for the Son of Man to be glorified" (John 12:23), when Christ no longer hid His purpose to reign as king from full view in the eyes of the public and of the government:  the Triumphal Entry, John 12:12-19.

Before the Triumphal Entry, Jesus did tell some to proclaim the gospel of faith in Christ to which His miracles bore witness, but He limited that proclamation's content, frequency, and extent, until the proper time when He commanded us to go into all the world, preach the gospel, make disciples of all nations, baptizing and teaching them to obey everything He commanded.  That proper time was after His resurrection, and particularly, after the Holy Spirit was poured out at Pentecost.

During His earthly ministry, Jesus trained His disciples to proclaim the gospel, but He did so in stages, in a limited manner, during the time of His humiliation, and we must learn our gospel proclamation today from that training.  But now, during the time of His exaltation, He commands us to go forth and proclaim the gospel as He has trained us to do.  This is how these two stages of Christ's ministry--humiliation and exaltation--and these two sets of instructions--"tell them" and "tell no one"--are connected in regard to their impact on our gospel proclamation today.