The essence of Christianity is to live out the life of another person called Christ. The reasons why the early Christians were called Christians in the first place was because their behavior depicted the person of Christ. They behaved so much like Jesus that it became obvious that People began to call them Christians.
Galatians 2.17
But if, while we seek to be justified by Christ, we ourselves also are found sinners, is therefore Christ the minister of sin? God forbid.
The scripture above summarizes the life that we are called to live as Christians. You are to live the life of Christ outside the Church and not just when we come to a church service. A lot of people get it all wrong. It takes a lot more than just attending a church service that makes us qualified to be called Christians.
To manifest Christ to the world simply means to apply the principles of holiness, consecration and obedience in our daily living.
2 Corinthians 5.20
Now then we are ambassadors for Christ, as though God did beseech you by us: we pray you in Christ's stead, be ye reconciled to God.
We are to be the Jesus that the world sees today. We are meant to let the world see Jesus through the kind of life that we live on a daily basis. The Christian life is practically a lifestyle and not an off and on something.