To live to the glory of God and for the salvation of men is of ourselves quite beyond our reach. Ultimately God will call us great because we sought not great things for ourselves but lived to serve. Christ organizes our lives around some other motive that personal gain and profit. Christ will examine us for this, not for how we did socially, economically, or politically. Christ's idea of happiness and success is to be useful, to be servants to our neighbors.
Happiness is the inevitable result of a certain kind of life the servant life.
The proof of this comes from the Man of Nazareth.