To the Overcomer...Sardis

Today, as we continue our series on the Lord's seven letters to the seven churches, we are more than halfway through these seven letter as we come to Sardis. Earlier the first churches all dealt with false teaching, paganism and idolatry. Today, we are looking at a church that Jesus corrects because they have fallen asleep. Jesus tells them they need to wake up. What is repentance? Why is it important, and why does the Lord bring it up in every letter that we have considered so far?