The discerning of Gods "incomparably great power" was beyond the understanding or "seeing" of the Ephesians. Paul asked God to fill them with His spirit so that they would believe in Him and, therefore, see more than they could possible comprehend without his spirit.
This incomparable power is for those of us who believe. It operates in all of us who believe in Him.
The miraculous event that Paul uses as an example of this incomparable great power was the Resurrection. The most awesome display of this great power of His!