You know it's funny... Nouwen's book got me thinking about eschatology... weird, I know...
It seems that your vision of Jesus can be greatly manipulated by how you expect Jesus to return. It would seem that someone who expects Jesus to return on a white horse wielding a great sword would have some inner conflict with the principals that Nouwen is teaching--principals of downward mobility, those are embodied by Christ on the cross. People who expect Jesus to come with great power and relevance might have trouble accepting that following Christ means the opposite. In other words, people who expect Jesus to come in a fashion opposite of that in which he came the first time might have trouble following the Jesus of the gospels. Which Jesus should we follow?
The book of Revelation should seem quite ironic to us... but that irony is often lost on those who insist on taking it literally. In chapter 5 the angel says "look, the lion" and so we expect a lion. But what is actually there? A lamb, and a slain one at that. How ironic. But some of us still expect a lion. We look around the lamb, hoping that a lion is really on the way. The true victory of Revelation, indeed the true victory of God is not through conquest, not through relevance, popularity, or power but through a slain lamb--a poor homeless man from Nazareth who died on a Roman cross.
That's it... that's the victory! The fullness of God (that means all of God, which means we need look no further to find God) was dwelling in that man! What a wonderful mystery! Perhaps we can only know it when we see it.
"For in Christ all the fullness of the Deity lives in bodily form" (Colossians 2:9). "Your attitude should be the same as that of Christ Jesus: Who, being in very nature God, did not consider equality with God something to be grasped,but made himself nothing..."(Philippians 2:5-7).
Therefore being part of that victory means embodying it, living it out, implementing it by being the body of that poor man from Nazareth. It means doing small things with great love. It means putting others before us. It means resisting the temptation to be fearful and to act out of fear when it seems like we're losing control. Indeed, being out of control is the Christian's state of residence.
We can only catch the irony of Revelation--that, knowing the Jesus who rode on a Donkey, the white horse description is humorous--if we can understand that ALL of God was in Jesus of Nazareth--God is like Jesus. When we've internalized that truth then all our eschatological expectations will conform to it as well. We will truly have the freedom to embody the crucified Christ rather than a king on a white horse, because the whole mystery of God is revealed in him and all the world's hope for the future is wrapped up in him, just as he is. We can truly embrace a life of downward mobility.