If we were allowed, when we migrated from this life, to live forever in the islands of the blessed, as fables tell, what need were there of eloquence when there would be no trials, or what need, indeed, of the very virtues themselves? For we should not need fortitude when nothing of either toil or danger was proposed to us; nor justice, when there was nothing of anybody else's to be coveted; nor temperance, to govern lasts that would not exist; nor, indeed, should we need prudence, when there was no choice offered between good and evil. We should be blessed, therefore, solely by learning and knowing nature, by which alone also the life of the gods is praiseworthy. And hence we may perceive that everything else is a matter of necessity, but this is one of free choice.
This is from Cicero's Hortensius. The Hortensius is unfortunately one of the works of Cicero that has not survived, but St. Augustine was influenced by it and preserved some quotations. The above quotation is found in De Trinitate XIV.12. The Latin is:
Si nobis, inquit, cum ex hac uita migrauerimus, in beatorum insulis immortale aeuum, ut fabulae ferunt, degere liceret, quid opus esset eloquentia, cum iudicia nulla fierent; aut ipsis etiam uirtutibus? Nec enim fortitudine egeremus, nullo proposito aut labore aut periculo; nec iustitia, cum esset nihil quod appeteretur alieni; nec temperantia, quae regeret eas quae nullae essent libidines; nec prudentia quidem egeremus, nullo delectu proposito bonorum et malorum. Vna igitur essemus beati cognitione naturae et scientia, qua sola etiam deorum est uita laudanda. Ex quo intellegi potest, cetera necessitatis esse, unum hoc uoluntatis.