A portion of a passage from Arcana Coelestia ~ Emanuel Swedenborg
When man is being regenerated, he receives life from the Lord; for before this he cannot be said to have lived, the life of the world and of the body not being life, but only that which is heavenly and spiritual. Through regeneration man receives real life from the Lord; and because he had no life before, there is an alternation of no life and of real life, that is, of no faith and charity, and of some faith and charity; no charity and faith being here signified by "cold" and some faith and charity by "heat."As regards this subject the case is this: Whenever man is in his corporeal and worldly things, there is then no faith and charity, that is, there is "cold" for then corporeal and worldly things, consequently those which are his own, are at work, and so long as the man is in these, he is absent or remote from faith and charity, so that he does not even think about heavenly and spiritual things. The reason of this is that heavenly and corporeal things can never be together in a man, for man's will has been utterly ruined. But when the things of man's body and will are not at work, but are quiescent, then the Lord works through his internal man, and then he is in faith and charity, which is here called "heat." When he again returns into the body he is again in cold; and when the body, or what is of the body, is quiescent, and as nothing, he is then in heat, and so on in alternation. For such is the condition of man that heavenly and spiritual things cannot be in him along with his corporeal and worldly things, but there are alternations. This is what takes place with everyone who is to be regenerated, and it goes on as long as he is in a state of regeneration; for in no other way is it possible for man to be regenerated, that is, from being dead to be made alive, for the reason, as already said, that his will has been utterly ruined, and is therefore completely separated from the new will, which he receives from the Lord and which is the Lord's and not the man's. Hence now it is evident what is here signified by "cold and heat."
That such is the case every regenerated man may know from experience, that is to say, that when he is in corporeal and worldly things, he is absent and remote from internal things, so that he not only takes no thought about them, but feels in himself cold at the thought of them; but that when corporeal and worldly things are quiescent, he is in faith and charity. He may also know from experience that these states alternate, and that therefore when corporeal and worldly things begin to be in excess and to want to rule, he comes into straits and temptations, until he is reduced into such a state that the external man becomes compliant to the internal, a compliance it can never render until it is quiescent and as it were nothing.
The last posterity of the Most Ancient Church could not be regenerated, because - with them the things of the understanding and of the will constituted one mind; and therefore the things of their understanding could not be separated from those of their will, so that they might in this manner be by turns in heavenly and spiritual things, and in corporeal and worldly things; but they had continual cold in regard to heavenly things and continual heat in regard to cupidities, so that they could have no alternation.
(Arcana Coelestia 933)