Sophocles's original Greek text was written in meter –while the dialogue was spoken, the choral odes were actually sung on stage. Sophocles used different meters to express different moods. If you get your hands on a good translation, reading the Chorus lines aloud should reveal this intentional setting of tone.
On that note, remember that the style of the English translation is going to vary from translator to translator. David Raeburn, for example, in the Penguin Classics edition, sometimes imposes a jarringly modern slant into the otherwise majestic prose (our favorite was the "No pain, no gain" line Electra delivers to her sister). Whatever edition you use, keep in mind that the way you're reading the play today is very different from how the play would have been preformed in Ancient Greece.