I find Revelation 3:15-16 interesting in that it is one of those passages warning us about our salvation right before the Church is Raptured at the end of Chapter 3 and beginning of Chapter 4.
Repentance is a change of mind that leads to a change of action. For Christians, that change of mind is the recognition that only Christ can live this thing we call the Christian life. And the change of action is then our allowing for the outworking of Christ's life in us and through us. That IS the basic objective of the book of Revelation, to call Christians in all churches in every age to repentance from the sin of religiosity, the substitution of our actions for God's action.