“Faith is the acceptance of a gift at the hands of Christ. … It is a very wonderful thing; it involves a change pf the whole nature of man; it involves a new hatred pf sin and a new hunger and thirst after righteousness. Such a wonderful change is not the work of man; faith itself is given us by the Spirit of God. Christians never make themselves Christians; but they are made Christians by God.
…It is quite inconceivable that a man should be given this faith in Christ, that he should accept this gift which Christ offers, and still go on contentedly in sin. For the very thing which Christ offers us in salvation from sin -not only salvation from the guilt of sin, but also salvation from the power of sin. The very first thing that the Christian does, therefore, is to keep the law of God; He keeps it no longer as a way of earning his salvation – for salvation has been given him freely by God – but he joyously as a central part of salvation itself. The faith of which Paul speaks is, as Paul himself says, a faith that works through love; and love is the fulfilling of the whole law…. The faith that Paul means when he speaks of justification by faith alone is a faith that works.
-J. Gresham Machen
 From: “Faith Works; The Gospel According to the Apostles, Macarthur,pg. 37; J. Greshem Machen, “What is Faith?,” New York: Macmillan, 1925, pg. 203-4