From The Gospel of Mark, by Mary Healy, commenting on Mark 1:1-8
The first verse of the Gospel is a title to the whole work. Like Matthew and John, Mark opens with an echo of the book of Genesis. The beginning recalls the first line of the creation narrative in Gen 1:1, and suggests that the good news that Mark is about to tell is a new beginning, a new work of God as original and stupendous as the creation of the universe.
What does gospel mean here? The Greek word euangelion (root of the English word evangelize) means “good news” or “joyful tidings,” and often referred to festive public occasions such as a military victory or the coronation of the emperor. An inscription from about 9 BC calls the birthday of Caesar Augustus “good news for the world.”
For the Old Testament prophets, especially Isaiah, the “good news” is not a past event but a promise that God is coming to save his people:
Go up onto a high mountain,
Zion, herald of glad tidings;
Cry out at the top of your voice,
Jerusalem, herald of good news!
Fear not to cry out
and say to the cities of Judah:
Here is your God! (Isa 40:9; see Isa 52:7; 61:1)
Mark’s announcement of “the beginning of the good news” is a resounding proclamation that now, in Jesus, the long-promised visitation of God has begun. The gospel is something to be preached (1:14; 13:10; 14:9; 16:15) and believed in (1:15). Indeed, so good is this good news that it is worth more than life itself (Mark 8:35; 10:29–30).
What is the content of this good news? In a word, it is that Jesus is the Christ, the Son the God.