『エチカ』、第V部、定理39

He, who possesses a body capable of the greatest number of activities, is least agitated by those emotions which are evil (IV. xxxviii.)--that is (IV. xxx.), by those emotions which are contrary to our nature; therefore (V. x.), he possesses the power of arranging and associating the modifications of the body according to the intellectual order, and, consequently, of bringing it about, that all the modifications of the body should be referred to the idea of God; whence it will come to pass that (V. xv.) he will be affected with love towards God, which (V. xvi.) must occupy or constitute the chief part of the mind; therefore (V. xxxiii.), such a man will possess a mind whereof the chief part is eternal. Q.E.D.

Since human bodies are capable of the greatest number of activities, there is no doubt but that they may be of such a nature, that they may be referred to minds possessing a great knowledge of themselves and of God, and whereof the greatest or chief part is eternal, and, therefore, that they should scarcely fear death. But, in order that this may be understood more clearly, we must here call to mind, that we live in a state of perpetual variation, and, according as we are changed for the better or the worse, we are called happy or unhappy. For he, who, from being an infant or a child, becomes a corpse, is called unhappy; whereas it is set down to happiness, if we have been able to live through the whole period of life with a sound mind in a sound body. And, in reality, he, who, as in the case of an infant or a child, has a body capable of very few activities, and depending, for the most part, on external causes, has a mind which, considered in itself alone, is scarcely conscious of itself, or of God, or of things; whereas, he, who has a body capable of very many activities, has a mind which, considered in itself alone, is highly conscious of itself, of God, and of things. In this life, therefore, we primarily endeavour to bring it about, that the body of a child, in so far as its nature allows and conduces thereto, may be changed into something else capable of very many activities, and referable to a mind which is highly conscious of itself, of God, and of things; and we desire so to change it, that what is referred to its imagination and memory may become insignificant, in comparison with its intellect, as I have already said in the note to the last Proposition.