The future will be met by the same reason. The argument against anxiety for the future is not "it will all work out" but an inventory of equipment: when the future becomes present, you will arrive at it "carrying TERMthe very same reason" (φέρων τὸν αὐτὸν λόγον) with which you now handle TERMwhat is present. Anxiety imagines the future as an unarmed man's meeting with a monster; Marcus reminds you that unarmed you will not be — the instrument is one and the same, and it is always with you. The only thing anxiety actually accomplishes is to spend today's reason on tomorrow's phantoms — spoiling the one moment in which reason really operates.

ἐὰν δεήσῃ — "if need be." A quiet reservation with a double bottom: one must still live to see the future. It may "not be needed" — death may settle the question first. This is not gloom but a strengthening of the argument: to tremble over what may never arrive at all is a double waste. Cf. the school's habitual reservation (ὑπεξαίρεσις — "with exception"): every plan for tomorrow the Stoic states conditionally.

Not a ban on preparation — a ban on trembling. The passage does not cancel the rehearsal of evils (Sen. Ep. 24): praemeditatio is performed now, with today's reason, precisely so that the future never arrives "unseen." What is forbidden is something else — ταράσσεσθαι, trembling before the non-existent. The exact twin is 8.36: do not gather into "now" all the coming burdens at once; to each portion of time its own reason will be given. The governing discipline is desire (fear of the future is a disease of desire); the sustaining one, assent (the future is "fearful" only by judgment).