Jesus does not begin his address to this church with a compliment, but instead He rebukes them. They had a good reputation in man's eyes, but to the LORD they were dead.

To be dead indicates no struggle, no fight, no persecution. A dead body has lost the battle, and the fight seems over. Being dead the church in Sardis presented no threat to Satan's domain. So it wasn't worth attacking.

In spite of the church in a general sense being dead, there was a godly remnant in the church of Sardis. There were some "which had not defiled their garments." Jesus says that "they are worthy." They were worthy, because they had been saved.