Learn Russian: Мы должны закончить эту книгу к среде ради нашего престижа. - We must finish this book by Wednesday for the sake of our prestige.

Both ради and для take the Genitive case, but they have different nuances. Ради strongly translates to "for the sake of," showing a high motivation, ultimate purpose, or sacrifice. Для is a more standard "for" used for general beneficiaries or practical purposes. Using ради here emphasizes that prestige is the ultimate driving force behind meeting the deadline.

Why is the preposition к used with среде, and what case is this?

Среде is the Dative form of среда (Wednesday). When expressing a deadline in Russian, к plus the Dative case translates to "by" a certain time. It shows that the action needs to be completely finished before or exactly when Wednesday arrives.

Since we are talking about an obligation, could we use the imperfective verb заканчивать instead of закончить?

No, because the sentence features a strict deadline (к среде). When a deadline is involved, the focus is entirely on the successful result and completion of the action, which requires the perfective verb закончить.

I have sometimes seen ради placed after the noun. Is нашего престижа ради possible here?

Yes! Ради is one of the very few Russian prepositions that can legally follow the noun it modifies. Saying нашего престижа ради is grammatically correct and adds a slightly dramatic or emphatic stylistic flair, though the standard before-the-noun placement used in this sentence is more common for everyday speech.