The Westminster Standards (Presbyterian Confessions) and the Three Forms of Unity (Reformed Confessions) are so very close in so very many ways. One area that some have highlighted a difference is the point where the WCF calls prayer a means of grace while the Heidelberg does not go that far.
For example, the Westminster Larger Catechism says the outward and ordinary means that Christ uses to communicate his blessings include all his ordinances, especially the word, sacraments, and prayer – all of these [his ordinances] are made effectual to the elect for their salvation (Q/A 154). The Heidelberg, a bit differently, says that prayer is the most important part of the thankfulness that God requires from us, and that God only gives grace and his Spirit to those who pray asking and thanking God for these gifts (Q/A 116). Prayer is in the third section of the Heidelberg, the “Christian living” or “gratitude” section and not in the word/sacraments section (the middle section on “grace” or “salvation”).
Though these differences should certainly not drive a wedge between the two confessions, it is interesting to think about. In his section on the means of grace in Reformed Dogmatics IV, Herman Bavinck is helpful. He said there is a certain sense in which the means of grace are broader, or wider, than just preaching and the sacraments: faith, conversion, struggles against sin, and prayer are included. However, it is better, noted Bavinck, to define the means of grace as objective, “external, humanly perceptible actions and signs that Christ has given his church and with which he has linked the communication of his grace” (RD IV.447-8). In other words, broadly speaking there are more than two means of grace, yet narrowly there are just two.
Bavinck used this “broad” and “narrow” concept in keeping with the Reformed scholastics. Richard Muller, in his excellent Dictionary of Latin and Greek Theological Terms (Grand Rapids: Baker Books, 1985), also notes this distinction. Under stricte (strictly or tightly), and late (loosely or generally), Muller said that the scholastics purposely and knowingly used definitions very precisely sometimes, while generally other times (p. 290). Perhaps this is helpful in our discussions of the means of grace. Were the Westminster divines speaking strictly or loosely? Would utilizing these distinctions help “harmonize” the two confessions?