A Christian is a person who places their faith in Jesus Christ. This faith in Jesus Christ is a saving grace, whereby we receive and rest upon him alone for salvation, as he is offered to us in the gospel. Faith in Christ therefore involves knowledge, belief and trust. A Christian is one who turns from their sin and places their hope in Jesus Christ for deliverance from the wrath to come.
A quote from J. Gresham Machen:
“If you are dissatisfied with a relative goodness which is no goodness at all. If you are conscious of your sin, and if you hunger and thirst after righteousness, if you are dissatisfied with the world and are seeking the Living God, then turn to the Church of Jesus Christ. That church is not always easy to distinguish today. It is often hidden away here and there, found in groups of those who have been redeemed from sin, and are citizens of a heavenly kingdom. Wherever it is found, you must turn to that true Church of Jesus Christ for a message from God. The message will not be enforced by human authority or by the pomp of numbers, yet some of you may hear it. If you hear it and heed it, you will possess riches greater than the riches of all the world. The responsibility of the Church is to testify that this world is lost in sin, that the span of human life, nay all the length of human history, is an infinitesimal island in the awful depths of eternity, that there is a mysterious, holy, living God, Creator of all, upholder of all, infinitely beyond all, that he has revealed Himself to us in His Word, and offered us communion with Himself through Jesus Christ the Lord, that there is no other salvation, for individuals, or for nations, save this, but that this salvation is full and free, and that whosoever possesses it, has for himself and for all others to whom he may be the instrument of bringing it, a treasure, compared with which all the kingdoms of the earth, nay all the wonders of the starry heavens, are as the dust of the street. An unpopular message it is. An impractical message, we are told. But it is the message of the Christian Church. Neglect it, and you will have destruction. Heed it, and you will have life.”
J. Gresham Machen (1881-1937) was one of the most prominent defenders of the Christian faith in the early part of the twentieth century. He was also instrumental in the formation of the Orthodox Presbyterian Church.