Experience. In that experience lies joy and sorrow. The Soul came here for experience and it is this experience or struggle, that gives it meaning and pushes it along in the field of manifestation.
There is no 'greatest parts' in the sense that in the darkness or suffering, the Light is still there. Only dimmer, if you like. But it helps in the advancement of the Soul just as much as spiritual experiences. (Happiness or the 'good' parts) One may indeed be filled with Peace and Beauty and the other comes with pain, but both ultimately helps the Soul on its upward march to oneness with God.
So one can say:
1. Realisation - the process of getting to know God. Of course this includes life's struggles and experiences.
2. Revelation - the process of revealing God to others.
3. Manifestation - the process of serving and glorifying the Divine in the universe in which we live. Much peace.