"Christians" are in need of conversion. I say this because it seems that most Christians in our day do not actually know the Jesus of Scripture. When you look at a typical Christian in America, s/he talks about Jesus, but this Jesus seems very different than the one in the NT. What is needed in our day is a true conversion to the Jesus of the Bible.
Conversion requires us to repent-- to change course/direction. The question is what course or direction is Jesus asking us to turn from and to. This is where I think we in America have an inaccurate idea of Jesus and his gospel. The most immediate answer people will give is "to turn from sin and turn towards Jesus" or something like that... however, that is a very meaningless statement because we still have not figured out what turning to Jesus looks like and we will always still sin.
There is so much in the OT about turning from the idolatrous ways of the Egyptians, Canaanites, and Babylonians. The NT makes many, many references to Rome and Caesar. Even the phrase in Romans 10:9 about "the Lord Jesus" or "Jesus is Lord" is a spin on the common understanding in that day that Caesar is Lord. It would be simplistic just to say that this has to do with prostrating ourselves before Caesar, another idol, or even Jesus Christ. The reason is that the type of "lord" that your serving determines the kind of kingdom that you live in. The kind of kingdom determines the daily routines of life: who is in control, what laws govern life, how do we relate with our neighbors and our enemies, economics and politics, the poor and rich, etc.
Do we believe that Baal is in control or Jesus? If we believe Baal is then we will implement Baal values in our life-- values of violence and hyper-sexuality. If we believe that Pharoah is God, then we will implement Pharoah's values and actions-- domination of a particular people/race, domination of economic landscape, sort of a survival of the fittest. If we believe that Caesar is God, then we will believe in Pax Romana-- that the trade networks, jobs, and security that Rome brings through such a strong ruler is the way for the world. However, to serve Christ is to reject such idolatry and the values and ways that go along with such idolatry.
Jesus asked the people of his day to repent of their wicked ways-- this required a turn from sin in self and society. This requires a choice, do I believe in Pax Romana/Americana, do I believe in Pax "Alcohola" (peace from the bottle or some other drug), do I believe in Pax Utilitarianism (peace from pursuing what brings happiness to the greatest number of people), etc. Or do I believe in the Shalom of God-- a true peace from a way of life that models Jesus Christ?