“Sacraments are signs of God’s will toward us, not simply signs of the people’s will among themselves, and so it is right to define the New Testament sacraments as signs of grace. A sacrament consists of two parts, the sign and the Word. In the New Testament the Word is the added promise of grace. The promise of the New Testament is the promise of the forgiveness of sins, just as this text says [cf. Luke 22:19 and Matt. 26:28], ‘This is my body, which is given for you. . . .[T]his is the cup of the New Testament in my blood, which is poured out for many for the forgiveness of sins.’ The Word, therefore, offers forgiveness of sins. The ceremony is like a picture of the Word or a ‘seal,’ as Paul calls it [Rom. 4:11], that shows forth the promise. Therefore, just as the promise is useless unless it is received by faith, so also the ceremony is useless unless faith, which really confirms that the forgiveness fo sins is being offered here, is added. Such faith encourages contrite minds. Just as the Word was given to awaken this faith, so also the sacrament was instituted in order that, as the outward form meets the eye, it might move the heart to believe. For the Holy Spirit works through the Word and the sacrament.” Philip Melanchthon, Apology of the Augsburg Confession, Art. XXIV, 69-71. in The Book of Concord, eds. Robert Kolb and Timothy J. Wingert (Minneapolis 2000), p. 270-71.
Melanchthon describes the relationship between the sacraments, ceremonies, the promise of God’s Word, and faith here. Notice the similarities with Martin Luther’s use of Augustine’s definition of a sacrament. http://wp.cune.edu/matthewphillips/2013/05/31/augustine-luther-and-the-sacraments/