“After death the sensation is either pleasant or there is none at all. But this should be thought on from our youth up, so that we may be indifferent to death, and without this thought no one can be in a tranquil state of mind. For it is certain that we must die, and, for aught we know, this very day. Therefore, since death threatens every hour, how can he who fears it have any steadfastness of soul?”
section 74 http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A2007.01.0039%3Asection%3D74
Cato Maior de Senectute – On Old Age (44 BC)
Original
Post mortem quidem sensus aut optandus aut nullus est. Sed hoc meditatum ab adulescentia debet esse mortem ut neglegamus, sine qua meditatione tranquillo animo esse nemo potest. Moriendum enim certe est, et incertum an hoc ipso die. Mortem igitur omnibus horis impendentem timens qui poterit animo consistere?
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Marcus Tullius Cicero 180
Roman philosopher and statesman -106–-43 BCRelated quotes

Letter to a relative, (1861).
Context: I think I have fairly heard and fairly weighed the evidence on both sides, and I remain an utter disbeliever in almost all that you consider the most sacred truths [... ] I can see much to admire in all religions [... ] But whether there be a God and whatever be His nature; whether we have an immortal soul or not, or whatever may be our state after death, I can have no fear of having to suffer for the study of nature and the search for truth.

Section 8 : Suffering and Consolation
Founding Address (1876), Life and Destiny (1913)
Context: It is written that the last enemy to be vanquished is death. We should begin early in life to vanquish this enemy by obliterating every trace of the fear of death from our minds. Then can we turn to life and fill the whole horizon of our souls with it, turn with added zest toall the serious tasks which it imposes and to the pure delights which here and there it affords.

Source: The Tales of Alvin Maker, Red Prophet (1988), Chapter 17.

Section 8 : Suffering and Consolation
Life and Destiny (1913)

Source: Reflections and Maxims (1746), p. 173.

“We trouble our life by thoughts about death, and our death by thoughts about life.”
Source: The Essays: A Selection