The Scriptures are fully sufficient to guide us to salvation, the worship of God and the godly life. We do not need to supplement Scripture with human traditions or philosophy, as if it were incomplete. However, it is important to understand that Sola Scriptura does not demand a simple kind of biblicism—believing nothing but what individual texts explicitly teach—as if that were ever actually possible. As the Westminster Confession of Faith describes:
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: unto which nothing at any time is to be added, whether by new revelations of the Spirit, or traditions of men. (I.VI.)
In that sense, as we read Scripture, explain Scripture, synthesise the teachings of Scripture and apply Scripture, we go beyond the words of the individual texts. We need to pull together what is “expressly set down in scripture” and drawing out what may, “by good and necessary consequence … be deduced from scripture.” But there lies the risk. It is very easy, in the process of doing theology, to run afoul of one possible interpretation of the maxim “Do not go beyond what is written” (1Cor. 4:6). For example, the Confession recognises that not all of Scripture is equally clear in its details (I.VII) and so those parts which are more mysterious should be understood in the light of those which are more plain (I.IX).
Biblical Language about God
This is especially true for language about God. The Scriptures use human language and human concepts to help us understand God. However, God the Father is neither biologically male nor is his relationship to God the Son anywhere near human procreation. This is the mistake that the Church of Jesus Christ of the Latter Day Saints makes, teaching that Christ is the actual progeny of Father God. Or some discussions about the persons of the Trinity rely too heavily on human social relationships and so risk implying that each person of the Trinity were a god in community with the others. Even descriptions of God’s love or grief are distinct from the human experience of emotions which is tied to our uniquely human psycho-somatic existence. As we handle any part of God’s word, and especially those parts which speak about God himself, we need to be careful not to stray too far from that which God has said. We need to be very, very confident that we are proceeding from “good and necessary consequence”.
Marriage, God and the Church
This is true of the parts of God’s word where his relationship to his people is described as, or likened to, marriage. This typology should not be pressed too far. We should carefully remain within the bounds of what Scripture says, lest we distort both our view of marriage and our view of God. For example, in 1 Corinthians 6:12-20, the sexual union is equated to union with Christ. But the point of similarity is a union leading to exclusivity and a dutiful faithfulness. It is not to draw particular details of comparison between sexual intercourse and union with Christ. Or again, in Ephesians 5, the point of typology is not actually marriage per se, let alone sexual intercourse in particular, but being one body. As a husband and wife become one flesh, so the church is Christ’s body:
Christ loved the church and gave himself up for her to make her holy, cleansing her by the washing with water through the word, and to present her to himself as a radiant church, without stain or wrinkle or any other blemish, but holy and blameless. In this same way, husbands ought to love their wives as their own bodies. He who loves his wife loves himself. After all, no one ever hated their own body, but they feed and care for their body, just as Christ does the church—for we are members of his body. “For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh.” This is a profound mystery—but I am talking about Christ and the church. However, each one of you also must love his wife as he loves himself, and the wife must respect her husband. (verses 25–33)
The apostle Paul merges the love command with a typology of Adam/Christ with a typology of body/one flesh to urge husbands to care for their wives. The application of the typology is the duty of husbands to selflessly love and care for their wives, both learning from and imperfectly pointing to the love of Christ for the church.
When Teresa of Avila’s mystic visions, or Puritan spiritual interpretations of the Song of Songs, or Josh Butler’s recent TGC USA article (now removed from the site with a redirect to the same content from the publisher’s site) begin to draw out too much spiritual significance from erotic love and even the act of making love, they too easily go beyond what is written. When such examples impute too much spiritual significance to erotic love, they go beyond God’s revelation, in a way that misrepresents both God and sexuality.
Theological Thinking Is Perilous Work
Theological thinking is good, necessary and important work. It honours God and his word as it seeks to understand Scripture’s meaning and significance. However, theology is a perilous business! The insights of Christian tradition, and the discernment and critique of fellow believers today are both valuable safeguards for us as we seek to do theology and biblical interpretation. For we must go about the task with reverence, caution and diligence, so that even as we draw out the good and necessary consequences, we do not go beyond what is written and drift too far into mere human speculation.
 This saying, quoted by the apostle Paul, somewhat ironically, is a difficult saying to understand in its original context: I’m not entirely sure that it is talking about the act of going beyond the teaching of Scripture.