by John Calvin
Moreover, there can be no question that man consists of a body and a soul; meaning by soul, an immortal though created essence, which is his nobler part. Sometimes he is called a spirit. But though the two terms, while they are used together differ in their meaning, still, when spirit is used by itself it is equivalent to soul, as when Solomon speaking of death says, that the spirit returns to God who gave it, (Eccles. 12:7.) And Christ, in commending his spirit to the Father (Luke 23:46), and Stephen his to Christ (Acts 7:59), simply mean, that when the soul is freed from the prison-house of the body, God becomes its perpetual keeper. Those who imagine that the soul is called a spirit because it is a breath or energy divinely infused into bodies, but devoid of essence, err too grossly, as is shown both by the nature of the thing, and the whole tenor of Scripture. It is true, indeed, that men cleaving too much to the earth are dull of apprehension, nay, being alienated from the Father of Lights (James 1:17), are so immersed in darkness as to imagine that they will not survive the grave; still the light is not so completely quenched in darkness that all sense of immortality is lost. Conscience, which, distinguishing, between good and evil, responds to the judgment of God, is an undoubted sign of an immortal spirit. How could motion devoid of essence penetrate to the judgment-seat of God, and under a sense of guilt strike itself with terror? The body cannot be affected by any fear of spiritual punishment. This is competent only to the soul, which must therefore be endued with essence. Then the mere knowledge of a God sufficiently proves that souls which rise higher than the world must be immortal, it being impossible that any evanescent vigour could reach the very fountain of life.
-- Institutes of the Christian Religion I:XV.2