Pure practical reason postulates the immortality of the soul, for reason
in the pure and practical sense aims at the perfect good (_summum
bonum_), and this perfect good is only possible on the supposition of
the soul's immortality. It is the moral law which determines the will,
and, in this will, the perfect harmony of the mind with the moral law,
is the supreme condition of the _summum bonum_. The principle of the
moral destination of our nature--that only by endless progress can we
come into full harmony with the moral law--is of the greatest use, not
only for fortifying the speculative reason, but also with respect to
religion. In default of this, either the moral law is degraded from its
holiness, being represented as indulging our convenience, or else men
strain after an unattainable aim, hoping to gain absolute holiness of
will, thus losing themselves in fanatical theosophic dreams utterly
contradicting self-knowledge.
For a rational, but finite, being the only possibility is an endless
progression from the lower to the higher degrees of perfection. The
Infinite Being, to whom the time-condition is nothing, sees in this
endless succession the perfect harmony with the moral law.