The message in book of Revelation to the church in Sardis is a spiritual alarm clock for a sleeping church (Rev. 3:1-6). This church is resting on the reputation of their previous accomplishments, sitting on a one point lead with two periods left to play. But God knows that this church is sleepwalking; that they are dead in their sins.
Sardis is in serious need of revival, to live again, and so Jesus comes to them as the one "who has the seven Spirits of God." This is a seven-fold concept of the Holy Spirit that reflects His ability to be wherever He needs to be. The church in Sardis needs the Holy Spirit because only the He is able to give life to a dying church (Eze 37:14).
But the church members in Sardis have their part to play as well. There are some things that only God can do to bring about revival, like pour out the Holy Spirit, but there are also some things that only we can do. So I take the next part of the message as sort of a "how to" manual for revival.
First, they must wake up, engage, and realize that a spiritual war is going on. Second, they must build from their strengths and not let these things slip as well. Finally they must realize that the game isn't over yet, that there is work left to do, otherwise it will be a very unpleasant surprise when the buzzer sounds.
True revival is grounded in Jesus Christ and what He has done for us. Revival does not replace our need of His salvation covering our sins nor our need to follow His example. Instead it seeks, by the power of the Holy Spirit, to live out the eternal life He has promised, making this future reality a present experience.