A very rough guide to Calvin's theology: Union with Christ

One of Calvin's key theological achievements was recognising the importance of the New Testament's teaching on union with Christ. He dismissed the medieval teaching on the value of human merit in salvation, insisting that God owes sinners nothing. Salvation comes through God graciously uniting us to Christ by his Spirit. In Christ believers receive the 'double benefit' of justification and sanctification. Justification and sanctification are conceptually distinct. Justification is God's declaration that a sinner is righteous in his sight on the basis of Christ's finished work, received by faith alone. Works don't come into it. In sanctification God sets us apart for himself and calls us to live to a holy life. By virtue of the believer's union with Christ, we are both justified and sanctified (Romans 5&6). It is impossible to have the one aspect of salvation apart from another. This pulls the rug from under the Roman Catholic charge that the Protestant doctrine of justification by faith alone is detrimental to good works. The faith which alone saves does not remain alone. As Paul said, faith works by love (Gal 5:6), or in the words of James, faith without works is dead (2:17). Let us then look to Christ and him alone for both justification and the transformation of our lives,

"In summary, [says Calvin] since in Christ all kinds of blessings are treasured up, let us draw a full supply from him, and none from any other quarter." (Institutes II:16:19).