The Gospel is a message that must be announced
We will start this week in Luke 4.14-21.
We see in this passage that Jesus was gathering a reputation as a teacher. Jesus is allowed to teach at this synagogue and is given the Isaiah scroll to read from. Jesus chooses Isaiah 61.1-2. From this passage we find that Jesus was "anointed" to preach the good news. To be anointed in the Old Testament meant to be set apart for devoted service to Yahweh.
His message was good news to the poor. (How was this message good news to the poor? Jesus is proclaiming the Year of Jubilee which was a cancellation of debts. Poverty doesn't only have to be financial.)
He proclaimed freedom from the prisoners. (How does his message accomplish this? See Acts 10.38).
It seems that in this chapter and others (Mark 1.35-39) that Jesus' primary mission (beyond his atoning death and resurrection) was to preach the message of the Kingdom of God.
As we look at other nuances of the gospel message and its proclamation, we turn to Luke 9.1-6.
In this passage we see that the gospel message is preached by followers of Jesus. This ministry is accomplished with the power and authority of Jesus (similar to his announcement of Kingdom of God being near; Mark 1.14-15). It is a message of the Kingdom of God. thus, the gospel was charged to Jesus' followers to go announce the Kingdom of God and it was done under the authority and power of Jesus (the King).
When looking at the passage where Jesus was anointed by a sinful woman at Bethany (Matt. 26.13) Jesus informs us that her story will be told within the gospel story. That is, the gospel will tell the whole story of Jesus' life and ministry and will (again) be told by others.
The last note on the proclamation of the gospel is that it will be preached to all the nations (see Matt. 24.14). In fact this mission must be carried out before Jesus returns. We see evidence of that in Revelation 7.9 that there will be members of nation, tribe, people and language.
It should be obvious, the word "euangellion" means good news, good report, good announcement. Therefore the gospel must be preached. It was preached by Jesus, it was (and should be) preached by his followers (with the authority and power of the one who sent them), it involves the whole story of Jesus and must be taken to all the nations.