Do you disagree that there is such a thing as the “covenant of grace,” or is your argument rather that infant baptism is not a proper implication from it?I wish I'd have written that. And come to think of it, Wellum might have done a bit of damage to another theological system along the way, without even trying.
What I argued in my chapter is that “the covenant of grace” is a misleading category. Let me explain it this way. It is beyond question that the theme of “covenant” is an important unifying theme in Scripture. However, if we are not careful the notion of the covenant of grace can flatten the biblical presentation of God’s plan of salvation in terms of biblical covenants. In truth, “the covenant of grace” is really a comprehensive theological category, not a biblical one. This does not mean it is illegitimate. After all, theological terms are often used in theology, which are not necessarily biblical terms—e.g., Trinity. However, the problem with the theological category—”the covenant of grace”—is that, if one is not careful, it tends to flatten the relationships between the biblical covenants across redemptive history without first allowing each covenant to be understood within its own redemptive-historical context, and then how each covenant relates to the other biblical covenants, and then how all the covenants find their fulfillment in Jesus Christ. I have no problem in using the category “the covenant of grace” to underscore the unity of God’s plan of salvation and the essential spiritual unity of the people of God in all ages. But if it is used, which I contend is the case in Reformed theology, to downplay the significant amount of progression and discontinuity between the biblical covenants, especially as fulfillment takes place in the coming of Christ, then it is an unhelpful term. In fact, I argued in my chapter that it would be best to place a moratorium on the category, especially if we want to make headway in the baptismal debate. In its place, we should speak of the one plan of God centered in Jesus Christ. And, furthermore, in speaking of the “covenant,” we must think in terms of the plurality of biblical covenants as we carefully unpack the relationships between the covenants across the canon. In short, it is imperative that we do a biblical theology of the covenants which, in truth, is an exercise in inter-textual relations between the covenants which, in the end, preserves a proper balance of continuity and discontinuity across the canon in regard to the biblical covenants. It is only when we do this that I am convinced we will make headway in our debate over the relationship between the biblical covenants without prejudicing the debate in one direction or the other.
Full interview here, as well as links to several other related resources. It's all well worth a read, and I suspect that any serious adherent of a traditional theological system will do well to interact with the argument of his forthcoming book with Gentry. In the meantime, here's the outstanding book his chapter was published in.