The history of Sardis is literally a “riches to rags” story. Sardis was a wealthy Lydian capital city, known for being impregnable — almost. Twice in their history there had been surprise assaults that caught them sleeping. They had not been keeping watch because by all appearances they were secure. Just as the city was living off a former but no longer existing fame, so the same attitude had infected the church. They are living in such a way as to cast doubt on their Christian identity; perhaps they truly needed the seven spirits to revive them. 
Scripture:   Revelation 3:1-6