Here’s a helpful note by Ligon Duncan on the Westminster Confession’s explanation of covenant theology. It’s found in the foreward of Covenant Theology: Biblical, Theological, and Historical Perspectives.
…The Westminster Standards set forth a bicovenantal structure of covenant, or federal, theology, with a covenant of works and a covenant of grace providing the theological outline of the biblical story of creation, fall, redemption, and consummation (WCF 7.2-3). That is, even though the chapter heading speaks of God’s covenant (singular) with man, the chapter itself makes it clear that there is a fundamental division and distinction between God’s covenant relations pre- and postfall. Both covenants, as an expression of his one eternal decree, have in view God’s glory and our good, our imaging him and communing with him, to the praise of his glory. But the means by which the covenants of works and grace are secured are distinct, with the covenant of grace dependent on the mediator in the fulfillment of its conditions.
To say this yet another way, the Westminster Confession’s presentation of covenant theology is not monocovenantal. It explicitly speaks of first and second covenants that are distinct: a covenant of works and a covenant of grace. Indeed, rightly understood, the covenant of works protects the grace of the covenant of grace.
From Oveido, FL