The gospel is a message of repentance. As Paul puts it in Galatians, it's the call to turn way from a life according to the flesh and to turn towards a life according to the spirit. Especially interesting is that the gospel is also the pathway to the kingdom of God on earth. In short, the gospel calls people to repent and promises to manifest the divine reality.
It operates on two levels, both as the critique of how we currently live and as the vision for how we ought to live. The vision always seems to display a picture that is utopian, a new world in which all problems are solved. The lamb will lay down with the lion, the hungry will be fed, the sick will be made well, etc. These kinds of images give hope to plenty of people that God cares and that God is going to act, and rightly so, but there's a catch. This utopian vision isn't separate from the call to repentance, but is necessarily linked with it. In fact, the call to repentance is the necessary prerequisite to the kingdom.
Perhaps a more clear way of looking at it is to say that the gospel is a call to repentance so that the kingdom of God can be real. All the biblical promises of a new world of peace, etc., are contingent upon the biblical call to repentance. Repent of your former way, live the new way, and you will see the kingdom of God.
Looking at it like this means that the gospel is universally addressed to the individual. That is, the gospel is not addressed to humanity as a whole, but is addressed to every human individual so that all of humanity will live in the divine reality. Ultimately, the response and responsibility is in each individual. No theocracy required. No hierarchy required. Just the single individual obeying the call to repentance.
(This post was brought to you by Kierkegaard and Badiou)