John Gill Commentary Mark 1:14

"Now after John was delivered up, Jesus came into Galilee, preaching the gospel of God," — Mark 1:14 (ASV)

Now after that John was put in prison
In the castle of Macherus, by Herod, for reproving him for taking his brother Philip's wife:

Jesus came into Galilee :
again, from where he came to be baptized of John:

preaching the Gospel of the kingdom of God :
the good news and glad tidings of the kingdom of the Messiah, or Gospel dispensation; which lies not in worldly pomp and splendour, in outward observances, in legal rites and ceremonies, but in righteousness, peace, and joy; in peace and pardon by the blood of Christ, in justification by his righteousness, and in free and full salvation by him.