1 John 3:10 (CB)

By this it is evident who are the children of God, and who are the children of the devil: whoever does not practice righteousness is not of God, nor is the one who does not love his brother.

The true Christian is one whose religion is in his heart and life. It is felt by himself in his heart. It is seen by others in his conduct and life. He feels his sinfulness, guilt and badness, and repents. He sees Jesus Christ to be that Divine Savior whom his soul needs, and commits himself to Him. He puts off the old man with his corrupt and carnal habits and puts on the new man. He lives a new and holy life, fighting habitually against the world, the flesh and the devil. Christ Himself is the cornerstone of his Christianity. Ask him in what he trusts for the forgiveness of his many sins, and he will tell you in the death of Christ. Ask him in what righteousness he hopes to stand innocent at the judgment day, and he will tell you it is the righteousness of Christ. Ask him by what pattern he tries to frame his life, and he will tell you that it is the example of Christ. But, beside all this, there is one thing in a true Christian which is eminently peculiar to him. That thing is love to Christ.

- JC Ryle