Quote Originally Posted by it-ogo View Post
OCS gave a set of Russian idioms, lightly influenced literary Russian vocabulary and grammar and almost did not influence spoken Russian (outside of those idioms).
If I'm not mistaken, the OCS influence also explains the long survival of the Cyrillic vowel ѣ (yat) in Russian, after it had disappeared from other Slavic languages. (And, allegedly, Bolshevik spelling reformers were eager to get rid of this letter because it "looked Biblical/religious".)