How Christians are to think about and interact with issues such as the transgender movement, the rise of social media, new science, or whatever, a thorough grounding in the truths of Scripture, truths which are expressly set down in its explicit teaching as well as derived from necessary consequences, will help us live wisely to God’s glory.
The Westminster Confession of Faith begins with what many have deemed some of the most well articulated statements concerning the doctrine of Scripture. And incorporated right into the confession’s understanding of Scripture is a brief, little clause on how one might do theology. The clause, which has garnered much thought over the centuries, was placed there as an expression defending the sufficiency of Scripture in all of life. In chapter 1, paragraph six, the Westminster divines state that “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 consequences may be deduced from Scripture…”
As Robert Letham has said, the phrase “by good and necessary consequences…is a profoundly important statement.” It points to the need for careful thought in reading, preaching, and thinking about the Bible.” In fact, he makes the point that “it mandates theology.” And Letham is right. No preaching or theological work can be done well unless the church is willing to deduce from Scripture good and necessary consequences. Louis Berkhof, commenting on the idea and history of dogma, writes that “the word dogma is derived from the Greek verb dokein. In classical Greek the expression dokein moi meant not only, ‘it seems to me’, or, ‘I am of the opinion’, but also, ‘I have come to the conclusion.’”  It is here then where we see the good and necessary function of theology and dogmatics; an enterprise of reason finding it’s authoritative grounding in God’s authoritative word.
To many people today, this idea of theology and dogma leaves a bad taste in their mouths, especially when connected to the idea of reasoning, necessary or not. William Cunningham, writing a little over 200 years after Westminster, noted that many express an extreme “dislike to precise and definite [theological] statements upon the great subjects brought before us in the sacred Scriptures. This dislike of precision and definiteness in doctrinal statements sometimes assumes the form of reverence for the Bible – as if it arose from an absolute deference to the authority of the divine word, and an unwillingness to mix up the reasoning and deductions of men with the direct declarations of God.” He continues though that “we believe it arises… from a dislike to the controlling influence of Scripture, [and] from a desire to escape…the authority… of [the Bible’s] regulating power as an infallible rule of faith and duty.” He concludes that “it has been the generally received doctrine of orthodox divines, and it is in entire accordance with reason and common sense, that we are bound to receive as true, on God’s authority, not only what is ‘expressly set down in Scripture,’ but also what, ‘by good and necessary consequences, may be deduced from Scripture.”
Theologians such as the Scottish puritan George Gillespie defended this way of logically reading Scripture by pointing to verses like Matthew 22:32 where Jesus himself defends his theology of the resurrection by quoting Exodus 3:6, “I am the God of Abraham, the God of Isaac, and the God of Jacob.” It is from this verse that Jesus necessarily deduces that the patriarchs, though long dead and buried, are actually alive, reasoning from the Exodus passage that “God is not the God of the dead, but of the living” (Matt. 22:32).
 Robert Letham, The Westminster Assembly, 139.
 Louis Berkhof, Systematic Theology, 18.
 William Cunningham, The Reformers & the Theology of the Reformation (Edinburgh, Banner of Truth, 2000) pp. 523
 ibid. 526