A person must think about more than just how his life wastes away each day. If he lives long, he cannot be sure his mind will stay sharp enough for careful thinking about business matters or deep reflection. These mental powers are what true knowledge of both divine and human things depends on. If his mind starts to fail, his breathing, eating, imagination, and desires may keep working fine. He will not lack these basic functions. But his ability to use himself properly, to see clearly what is right and just in all things, to correct wrong thoughts and sudden impressions — even to decide whether he should keep living — all these things that need the mind's best strength will be gone.
A man must not only consider how daily his life wasteth and decreaseth, but this also, that if he live long, he cannot be certain, whether his understanding shall continue so able and sufficient, for either discreet consideration, in matter of businesses; or for contemplation: it being the thing, whereon true knowledge of things both divine and human, doth depend. For if once he shall begin to dote, his respiration, nutrition, his imaginative, and appetitive, and other natural faculties, may still continue the same: he shall find no want of them. But how to make that right use of himself that he should, how to observe exactly in all things that which is right and just, how to redress and rectify all wrong, or sudden apprehensions and imaginations, and even of this particular, whether he should live any longer or no, to consider duly; for all such things, wherein the best strength and vigour of the mind is most requisite; his power and ability will be past and gone.