Life is the activity by which a being moves itself. The soul is the principle and the faculties and organs are the means of human activity. The word “life” is often used to designate the nature, the faculty, or the vital action of a particular being. Thus we speak of the vegetative life of a plant, of the sentient life of an animal, of the rational life of man, of the intellectual life of an angel, and of the divine life of God. Life is also used to designate man's earthly pilgrimage. In this sense it is a journey to eternity. "What is life?'' asks St. James. "It is a vapor which appeareth for a little while, and afterwards shall vanish away'' (James iv. 15).
As man is composed of body and soul, he has a physical and a spirit life. The former is temporal and changeable, the latter immortal and immutable. The body increases, decreases, and dies, but the soul lives forever.
Besides the natural life the soul of a Christian receives a supernatural life in holy Baptism. During his earthly career man may increase, decrease, or destroy this life of grace, even as he can care for or take his physical life.