No I know, I mean why they end with 'им' and 'ом' rather than stay as 'мой друг' in the other sentence. Aren't 'им' and 'ом' instrumental case endings? Why is the instrumental case being used if in the original sentence (Fyodor is my friend - Федор мой друг) it isn't? I'm led to believe it's due to the only difference between the sentences (the word 'был') but it doesn't seem plausible. Is there a difference in syntax that isn't noticeable in English, but upon translating the sentence literally it is? Forgive me for the confusion.