Selection from – Ethics – Part V. On the Power of the Intellect; or of Human Freedom (Page 11)
Spinoza's Words: (the rational mind is less subject to thoughts of death)
Proposition XXXVIII. In proportion as the mind understands more things by the second and third kind of knowledge, it is less subject to those emotions which are evil, and stands in less fear of death.
The mind's essence consists in knowledge therefore, in proportion as the mind understands more things by the second and third kinds of knowledge, the greater will be the part that is not touched by the emotions, which are contrary to our nature, or in other words, evil.
Note.—Hence we understand that point which I touched on in Part IV. and which I promised to explain in this Part; namely, that death becomes less hurtful, in proportion as the mind's clear and distinct knowledge is greater. Again, since from the third kind of knowledge arises the highest possible acquiescence, it follows that the human mind can attain to being of such a nature, that the part [which] perishes with the body should be of little importance when compared with the part which endures. But I will soon treat of the subject at greater length.
Comment:
The more the mind is filled with the products of reason the less it is impaired by the emotions. In other words, reason can control the emotions.
In Spinoza's time most of the population's greatest concern was what was going to happen to them after their deaths. Their religious leaders where constantly exhorting them to consider it. Spinoza would relieve them of the enslavement to that mental anxiety and lead men to freedom though the use of reason (knowledge of the second and third kind).
He hints here of a part of the mind that "endures," which he says he will speak of later. In Proposition XXIII (Page 7 and 8) he says the "human mind cannot be absolutely destroyed with the body, but there remains of it something which is eternal."