As one contemplates, penetrating deeper and deeper into the nature of reality, one leaves the sensible world behind, transcends the subject/object mode of perception, and experiences one's soul.
I have found that the greatest degree of inner tranquility comes from the development of love and compassion. The more we care for the happiness of others, the greater is our own sense of well-being. Cultivating a close, warmhearted feeling for others automatically puts the mind at ease.