Spiritual heat comes from no other source than the sun of the spiritual world. For there is a sun there which comes forth from the Lord, who is in the midst of it. Since it is from the Lord, that sun in essence* is undiluted love. This sun looks to the angels like a fire, exactly as the sun of our world does to us. This fiery appearance is because love is spiritual fire. This sun radiates heat and light, but since this sun is undiluted love, the heat it produces is in essence love, and the light it produces is in essence wisdom. This makes it plain what the source of spiritual heat is, and that this is love.

[2] However, a few remarks must be made about the source of spiritual coldness. This comes from the sun of the natural world, and from its heat and light. The sun of the natural world was created so that its heat and light could receive into themselves spiritual heat and light, and convey these through the atmospheres to the final level on earth. This was so that they could carry out the Lord's purposes which He intends in His own sun, and also could cover spiritual things with suitable clothing, that is, materials, in order to execute His ultimate purposes in nature. These results take place when spiritual heat is combined with natural heat. But the result is the reverse, when natural heat is separated from spiritual heat, which is the case with those who love natural things and reject spiritual ones. In their case spiritual heat turns into spiritual coldness. The reason why those two kinds of heat,** created to be in harmony, become so opposed is that then the master heat becomes the servant heat, and vice versa. To prevent this happening, spiritual heat, which is by its lineage the master, withdraws; and then in these cases spiritual heat grows cold, because it becomes its opposite. These considerations make plain the nature of spiritual coldness, as being deprived of spiritual heat.

[3] In what has just been said heat is understood to mean love, because that heat is felt by living*** things that it affects as love. I have been told in the spiritual world that purely natural spirits feel an intense cold, when they come alongside an angel who is in a state of love. Likewise the spirits of hell, when heat from heaven reaches them; yet among themselves, when the heat of heaven is shut off from them, they broil with great heat. * The original says 'in its coming to be', but this appears to be a mistake for 'in essence.' Cf. 380:11, TCR 33. ** Reading calores 'heats' for amores 'loves'. *** Reading in subjectis viventibus for in subjectis vivens.