Speaking of God, we are touching precisely on the subject which, in Jesus' earthly preaching, was his main focus. The fundamental subject of this preaching is God's realm, the "Kingdom of God". This does not mean something that will come to pass at one time or another in an indeterminate future. Nor does it mean that better world which we seek to create, step by step, with our own strength. In the term "Kingdom of God", the word "God" is a subjective genitive. This means: God is not something added to the "Kingdom" which one might even perhaps drop.
God is the subject. Kingdom of God actually means: God reigns. He himself is present and crucial to human beings in the world. He is the subject, and wherever this subject is absent, nothing remains of Jesus' message.
Therefore, Jesus tells us: the Kingdom of God does not come in such a way that one may, so to speak, line the wayside to watch its arrival. "The Kingdom of God is in the midst of you!" (cf. Lk 17: 20ff.).
It develops wherever God's will is done. It is present wherever there are people who are open to his arrival and so let God enter the world. Thus, Jesus is the Kingdom of God in person: the man in whom God is among us and through whom we can touch God, draw close to God. Wherever this happens, the world is saved.
[Pope Benedict, to the Roman Curia 22 December 2006]