Before Mark gets into the actual teaching of Jesus, he first winds up John’s ministry, by telling us John was imprisoned. It may give us a false impression that what comes afterward in Mark 1:16-45 actually occurred after John’s imprisonment, but this isn’t so. We’ve all seen movies and TV programs that begin by showing us a tragedy, and then words come up on the screen saying something like… Six months earlier… In other words the program backtracks in order to give us a context in which the tragedy took place. Something similar occurs in the first chapter of Mark. John is put in prison. Thus, his ministry ends, after which Mark settles into telling us what Jesus said and did during the 6-8 months prior to that time (Mark 1:16-45; plus Mark 2 and 3).
In Mark 1:14 we are told that Jesus returned to Galilee preaching the Gospel of the Kingdom of God, but John places this event well into Jesus’ ministry at John 4:1. Jesus left Judea even before his disciples had a chance to purchase food supplies for the journey (John 4:8). Moreover, he went through Samaria, rather than the normal route between Galilee and Judea. Something occurred here that isn’t being told outright. Jews have no dealings with Samaritans (John 4:9), so it seems Jesus had to leave in a hurry and took the route the Pharisees would be least likely to use, if they tried to follow him (John 4:1). The Gospel of John doesn’t record the Baptist’s actual imprisonment, but it does tell us John wasn’t in prison after Jesus celebrated the Passover of John 2 (John 3:23-24). Thus, he implies the day of John’s confinement was very near. The fact that John 4:1 records Jesus leaving Judea, because the Pharisees believed he baptized more people than John, implies that they were behind John’s imprisonment (cp. Mark 3:6: 6:17-19; 12:13), which, no doubt, had just taken place, possibly in the context of the Herodians telling Herodias what John told them under the guise of a religious discussion.
Whatever the circumstances that led up to John’s incarceration, we are told that, after that event, Jesus returned to Galilee from Judea and preached the Gospel of the Kingdom, saying: “the time is fulfilled…” What time was fulfilled? Luke records Jesus saying, “The Law and the prophets were until John, since that time the Kingdom of God is preached” (Luke 16:16). In other words the Old Covenant ends with John’s imprisonment, although there was a brief season (cir. 40 years), when the Jewish rulership sought to change the times (cp. Daniel 7:25) and keep the Old Covenant in force. They sought to keep the Old Covenant in force, while the Apostles preached the New Covenant. However, in essence the Law and the Prophets ended with John. He fulfilled that time and pointed to Jesus who would bring in the new age. Therefore, the Kingdom of God was at hand, and Jesus told the people to believe the good news (Matthew 1:14-15).
There was, also, a brief period of time when the ministries of John and Jesus overlapped. From the time of Jesus’ baptism (Mark 1:9-11) to his return into Galilee (Mark 1:14) took about a year, but from Jesus’ baptism to the time when he left Judea and entered Samaria (John 4:1), presumably immediately after John’s imprisonment, it was about 8-9 months. So, that incorporated the period when both John’s and Jesus’ ministries overlapped. That is to say, if John’s imprisonment occurred shortly after the Passover of 28 AD (John 2) and about the time of Pentecost that same year (cp. John 3:23-24 and John 4:1), the beginning of Jesus’ ministry would have taken place near the autumn holy days of 27 AD or about eight to nine months prior to Herod’s arresting John. Thus, once John was imprisoned, the Old Covenant was fulfilled! Therefore, about one year after his baptism, Jesus returned to Galilee preaching “the time is fulfilled (cp. Galatians 4:4), the Kingdom of God is at hand, repent and believe the Gospel” (Mark 1:15).