Learn Swedish: Han skulle offra allt, men uppoffringen blev för stor. - He was going to sacrifice everything, but the sacrifice became too big.

This sentence is a helpful reminder of another very common use for för! When placed right before an adjective like stor (big), för means "too". So för stor means "too big". It is completely separate from the för ... skull construction.

The verb is offra (to sacrifice). Why is the noun uppoffringen and not just "offret"?

While the noun ett offer does exist, it usually translates to "a victim" or a literal, physical sacrifice. When talking about making a personal or emotional sacrifice (giving up time, comfort, or money), Swedish uses the noun en uppoffring.

Why is it skulle offra (would sacrifice) instead of just using a simple past tense verb?

Skulle is the past tense of ska (will / going to). Using skulle followed by the infinitive offra expresses the "future in the past"—it describes what he was going to do or intended to do before things changed.

Why use blev (became) instead of var (was) at the end of the sentence?