How does Keller describe the gospel in this chapter?

The gospel is a single formula with a number of points that must be recited to everyone, in every time and place.

The gospel is different for every person who hears it$,$ because at bottom, it has no real message of its own.

The gospel is a clear and present word, but it is not a simplistic word. There is a singular, universal truth to its message that is the same for all people, but there is also an irreducible complexity in how that message is presented.