245. It will now be explained what is the nature of the influx of light into the three degrees of life in man which belong to his mind. The forms which are receptacles of heat and light, that is, of love and wisdom in man, and which, as was said, are in threefold order, or of three degrees, are transparent from birth, and transmit spiritual light just as crystal glass transmits natural light. Hence it is that man as to his wisdom can be raised even to the third degree. But yet these forms are not opened, except when spiritual heat conjoins itself to spiritual light, that is, love to wisdom. By this conjunction these transparent forms are opened according to degrees. It is the same with the heat and light of the sun of the world in respect to the plants upon the earth. The light of winter which is as bright as that of summer does not open anything in seed or in tree. But when spring heat conjoins itself to the light, then it opens [vegetation]. The case is similar, for spiritual light corresponds to natural light, and spiritual heat to natural heat.