Reread books. Seneca, Epistulae 1.2.3-4

A good book is one that you never cease to learn from. And you should read it slowly, savoring it as you would a good meal. You can hear me read this passage <here>.  

Non prodest cibus nec corpori accedit qui statim sumptus emittitur; nihil aeque sanitatem impedit quam remediorum crebra mutatio; non venit vulnus ad cicatricem in quo medicamenta temptantur; non convalescit planta quae saepe transfertur; nihil tam utile est ut in transitu prosit. Distringit librorum multitudo; itaque cum legere non possis quantum habueris, satis est habere quantum legas. 'Sed modo,' inquis, 'hunc librum evolvere volo, modo illum.' Fastidientis stomachi est multa degustare; quae ubi varia sunt et diversa, inquinant non alunt. Probatos itaque semper lege, et si quando ad alios deverti libuerit, ad priores redi. Aliquid cotidie adversus paupertatem, aliquid adversus mortem auxili compara, nec minus adversus ceteras pestes; et cum multa percurreris, unum excerpe quod illo die concoquas.

There is no benefit from nourishment expelled from the body immediately after it arrives. Nothing hinders health like a constant change in remedies. The wound attacked with medicine does not scar over. The plant that is always being moved never recovers. There is nothing so useful that it becomes beneficial only in passing. A multitude of books distracts you. As you cannot read all that you have, it is enough to have only what you might read. “But I just want to flip through (†) this one, then that one!” you say. Tasting many things is the mark of a weak stomach. A diverse diet at constant variance with itself corrupts; it does not nourish. Even so, read always the books whose worth you have already proven, and when the desire to turn to others strikes you, go back instead to your collection. Gather your books every day—one to help you against poverty, another against death, and others for different plagues. When you have looked through them all, take just one to digest for the day.

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(†) The Latin verb evolvere means literally to roll out. The books here are thus properly scrolls, rather than codices.