Early on in the Westminster Confession of Faith one reads, “The whole counsel of God concerning all things necessary for his own glory, man’s salvation, faith and life, is either expressly set down in Scripture, or by good and necessary consequence may be deduced from Scripture”(1:6). This phrase basically means that Reformed doctrine and practice are not simply derived from a set of proof texts, but from a deeper and more exhaustive interaction with Scripture. This interpretive method is quite essential to Reformed theology, as Ryan McGraw notes in his little booklet, By Good and Necessary Consequence.
“…The principle of good and necessary consequence as set forth in the Westminster Confession of Faith represents the result of the Reformed Protestant quest to justify the task of theology and to apply the Scriptures in a contemporary context for the edification of the church. Reformed hermeneutics both built upon and amended medieval methods of biblical interpretation. The medieval quadriga was replaced by an emphasis upon the literal and historical sense of the text with doctrinal, practical, and christological applications drawn from that sense by good and necessary consequence. In large part, the entire Reformed tradition of doctrine and preaching hinges upon this point” (p. 28).
This is a good little book (around 80 pages) that helps explain how Reformed doctrine is derived from Scripture. I’ve found it helpful in my context where very few people are familiar with Reformed theology. Many Christians are familiar with proof texts but don’t understand other interpretive principles like Scripture interprets Scripture and this one, “by good and necessary consequence.” Of course this has much to do with the doctrine of the Trinity, covenant theology, covenant baptism, the christological aspect of the Old Testament, and so forth. It’s a pretty important topic. Therefore, this book is a good resource that will help the reader understand and utilize this principle and also explain it to others who are unfamiliar with Reformed biblical interpretation.