620. That regeneration is impossible without the truths by which faith is formed, may be illustrated by the following comparisons. It is as impossible as a human mind without understanding; for the understanding is formed by means of truths, and therefore teaches what ought to be believed and what ought to be done, what regeneration is, and how it is effected. Regeneration without truths is as impossible as the vivification of animals or the growth of trees without light from the sun; for if the sun did not give light at the same time that it gives heat, it would become "like sackcloth of hair" (as described in the Apocalypse 6:12), and "black" (Joel 2:10, 31), and thus mere darkness would be upon the earth (Joel 3:15). It would be the same with man without truths, which send out light from themselves; for the sun from which the light of truths flows forth is the Lord in the spiritual world. If spiritual light did not flow therefrom into human minds, the church would be in mere darkness, or in shadow from a perpetual eclipse. Regeneration, which is effected by means of faith and charity, without truths that teach and lead, would be like navigation on the great ocean without a rudder, or without a mariner's compass and charts. It would also be like riding in a dark forest at night. The mind's internal sight with those who are not in truths but in falsities, which they believe to be truths, may be likened to the sight of those whose optic nerves are obstructed, the eye still appearing sound and capable of sight, although it sees nothing; which kind of blindness is called by physicians amaurosis and gutta serena; for in such the rational or intellectual faculty is obstructed above and open below only, owing to which rational light becomes like the light of the eye, and consequently all their opinions are imagination only and are fashioned from mere fallacies. And in such case men would stand like astrologers in the market-places with long telescopes, uttering unmeaning prophecies. Such would all students of theology become, unless genuine truths were disclosed by the Lord from the Word.