John Calvin referred to the double grace in his Institutes of the Christian Religion from the first edition to the last edition. Two important presuppositions of the double grace of John Calvin are the work of atonement of Jesus Christ and the work of the Holy Spirit through faith. Because the work of atonement in Jesus Christ is real, humanity can claim this as its own. But the work of the Holy Spirit is also needed, and even the work of atonement of Jesus Christ is of no use without the concept of the "union with Christ." But "the union with Christ" and the "the oneness of god and man" are perfectly opposite in conception. "Union with Christ" guides one toward humility, but the ``the oneness of god and man`` guides one toward life. Therefore "union with Christ" is opposed to the "the oneness of God and man." Calvin has no hesitation in agreeing with Martin Luther when considering justification by faith in the nature of a court proceeding. But Calvin says that sanctification with justification which leads to the "union with Christ only takes place by faith. We can receive the "double grace" in the "union with Christ." First, grace is a grace of justification made possible through Christ who is innocent, who appears before the gracious Father who is the Judge of heaven. Second, grace is the grace of sanctification in which we can live a pure life without flaw through the Spirit of Christ. In Calvin, the works of man are excluded, because both justification and sanctification are given by the grace of God, so that man cannot boast of anything. Therefore, it seems that John Calvin provides a solution to a problem which Martin Luther could not resolve, through the way that Calvin deals with justification and sanctification together. As a result, the challenge of meritorious sanctification in the Roman Church can be rejected, because the Christian soteriological system has been re-constructed by Calvin as the double grace through faith alone. God recognizes good works as perfectly sacred in Jesus Christ, even if they fall short before God`s eyes. The perfection of sanctification through the grace of God and the progression of sanctification as a fruit of the faith are harmonized through their complementary cooperation. Calvin testifies to the harmony between justification and sanctification, those double graces which only happen by faith. And he also testifies to the living biblical faith through the harmony of the perfection and the progression in sanctification. If we really understand the double grace of John Calvin which is received from the union with Christ only by faith, it can give us many benefits. First, it guides us to salvation through a living faith. Second, it guides us through the life of the cross and the denial of self. Third, this double grace helps us to seek reformation of the individual, the church, and the society. The world of the 21st century is calling Christians and churches to hold on to the real Christian faith and to live real Christian lives. In this situation, the double grace which is the main point of the soteriology of John Calvin will help to rebuild a living faith. And it is my hope that this living faith movement will expand to include a reformation in the social life of all humanity.