"Repent, for the kingdom of God is not right now but will be around after you die!"
Typically, this is not how we read the opening lines of Jesus' life in the gospel of Mark. However, I find that by and large that's how some people live. There is a sense that the promised kingdom of God will not see fullness until the afterlife, and because of this we can just get on with our lives now, living in the assurance that upon death we will be in the kingdom of God.
I see some key problems with this view, all of which can be highlighted by taking a different position: the Now.
First of all, Jesus' proclamation was about the here and now. "The kingdom of God is here," he proclaimed. Repentance was predicated upon the immanence of the kingdom, insisting that the kingdom was here, but always out of reach for the impenitent. "Today you will be with me in paradise," he said to the thief crucified with him. Today. The kingdom, as preached by Jesus, was a kingdom of now. The matter of the kingdom "not yet" I will deal with later.
Secondly, at the heart of the Christian proclamation is that the transcendent God was manifest in the physical and temporal in the person of Jesus of Nazareth. The word was made flesh and lived among us. This is the movement of God to us, not the movement of us to God. The direction of divine self-revelation is from the divine, not towards the divine. That movement, from eternal to temporal, is the movement to the now. Even the language that Jesus uses for the holy spirit is one of sending from God to humanity. The direction is again from the divine, from the eternal to the temporal.
Thirdly, Jesus' teaching is about how to live now. Forgive now. Make peace now. Give now. Love now. Any time that Jesus mentions a final judgement, it is too late for action. The state of play is frozen and complete, just as in death a human life is complete. Nothing more can be added to it. The life of the disciple is in the now.
And lastly (for this brief account), the presentation of the kingdom of God in the now and the not-yet is seen in the tension between the way of the flesh and the way of the spirit, the tension between what is and what ought to be. In enacting the kingdom, each and every Christian is caught between the world as it is (with all its faults and foibles) and the kingdom of God proclaimed by Jesus (with all its hope and answers). The "now" is the act that we make today, and the "not-yet" is the transformed life of the Church which, although universalising, has not yet reached all. It is the not-yet in the sense that the Church will continue to act.
The kingdom of God is now. So why wait until death to do what was commanded? Why wait until the afterlife to manifest God? The command of Christ is to manifest God in the here and now, not paying any heed to the there and then.