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Calvin and Luther believed free will does not co-operate with God's grace which, according to them, cannot be rejected (see monergism). The Lutheran Augsburg Confession says of baptism, "Lutherans teach that it is necessary to salvation and that by baptism the grace of God is offered and that children are to be baptized, who by baptism, being offered to God, are received into God's favor." The French reformer John Calvin expanded and further developed these Augustinian themes in his systematic "Institutes of the Christian Religion" in 1536.