What is biblical textualism? Is it a good thing or should Christians be warry of it?
Textualism and the Law
Textualism is a formalist theory in which the interpretation of the law is primarily based on the ordinary meaning of the legal text and where no consideration is given to non-textual sources, such as the intention of the law when it was passed or the problem it was intended to remedy, so textualism by itself is not bad, but what about textualism when referring to Scripture? I love what one Bible scholar said: “When the plain sense makes common sense, seek no other sense.” I would add, “Where the Bible is silent, so must we be.” Essentially textualism is sticking to the text of Scripture or taking it literally. Some define it as the taking of sentences, paragraphs, words, and phrases just as they appear in the text. Textualism is important for prosecutors, attorneys, judges, and juries because words, phrases, or sentences may be taken literally and be used as legal evidence, and be admissible evidence in a court of law, so there is nothing wrong with textualism. It is only when biblical textualism is taken to an extreme that it becomes a problem. 
The Obvious Meaning
When the meaning of Scripture seems clear, then that is how it should be understood. I have heard older, more experienced pastors say that we can spiritualize the truth away and miss the obvious meaning of Scripture, while at the same time, ignoring the clear meaning of the verses. It’s easy to spiritualize text when we see numbers, phrases, or certain accounts that make us think of something else in the Bible. One example is Jeremiah the Prophet who wrote to the nation of Judah and said, “For I know the plans I have for you,” declares the Lord, “plans to prosper you and not to harm you, plans to give you hope and a future” (Jer 29:11). Of course this is true and God does have a future hope for people, but this wasn’t written to us but for the nation Judah, so if we try to apply this to our life, we’re taking the text out of context and making it a pretext by applying it to ourselves. Of course, God does want us to prosper in all things (3 John 1:2), but even the context of that verse was not about financial prosperity, but about our health, including our spiritual health. This means that we are “walking in the truth” (2 John 1:3), so it’s not gaining financial wealth. If we knew the context of Jeremiah 29:11, we’d not want that plan because Judah was taken captive and would be under bondage for 70 years, so that’s not something we ought to be hoping is in our future. Context is king, so when we read verses, we can’t read into it or put our own meaning into them.
There are Bible verses that are prescriptive and Bible verses that are descriptive; some are both, but all of the Bible was written for us, but not all of the Bible was written specifically to us. A clear example is that of the sacrificial system. We do not need to sacrifice animals for the covering of sin because Jesus has taken away our sins by His own blood. When we read Scripture, we can neither spiritualize it’s meaning away or make it into an allegory. Jesus challenged the religious leaders to “search the Scriptures” (Mark 2, 12) to see “what’s written in the law” (Luke 10:26). He told them to read the Scriptures, so that the meaning would be clear to them. It can be a dangerous thing to read meaning into Scriptures (called “eisegesis”) when it’s not there. Here’s where textualism helps us get the right meaning. We take out of Scripture the obvious meaning (called “exegesis”) and give attention to the cultural, historical, and social setting of when it was written and to whom it was written. Certain things are timeless (John 3:16; 13:34-35), but some things were only for a time (Mark 14:12a). Jesus’ words are descriptive (of events) and prescriptive (apply to us). He describes how people can know who His disciples are (John 13:34-35), and practicing that kind of love is prescribed to us (1 John 3). We are tolod to die to ourselves and live for Christ but this doesn’t mean we have to die physically for Christ. It means we end our life as we know it and discover that we are not the center of the universe. We get a call from Copernicus and he tells us we’re not the center of the universe anymore. Jesus becomes the center of our life.
When the meaning is plain, we go with that meaning, but when there are difficult passages, we can look for other related Scriptures to make the meaning become clearer (hopefully). Sometimes the difficult passages can be understood by reading other Scriptures that deal with that same topic or subject. My old King James Bible has Scriptural references to other passages in my Bible listed for certain Scriptures. For example, where it says “the just shall live by faith” (Rom 1:17, Gal 3:11, Heb 13:3), I have another verse that refers to Habakkuk 2:4, where it says “the just shall live by his faith.” This shows that the gospel is spread throughout the Bible because it says that even Abraham “believed the LORD, and he counted it to him as righteousness” (Gen 15:6). Justification by faith is not new, because many of the Old Testament saints will be in the kingdom! One piece of advice I heard many years ago was this: “If it’s new, it’s not from God; if it’s from God, it’s not new,” and I’ve found that to be true. A “new teaching” from the Bible or a “word from God” can be fertile ground for heresy and error. Why not stick to what we know is true and that’s the whole counsel of God found in the whole Word of God, from Genesis to Revelation. We don’t have to guess what is true and what isn’t because God cannot lie and His Word is ever-true!
Textualism is an important thing to consider when reading Scripture, but we can go from one ditch to the other quite easily. We can spiritualize the meaning of some texts when the meaning is obvious, or we can allegorize other readings when they are clearly commands of God (i.e. Matt 25:35-36, 28:19-20). A fine example is that some believe that the Great Commission was only intended for the 12 Apostles, but there are just too many other Scriptures that tell us we are to be His witnesses…to be salt and light (Matt 5:13-16). We are told to love one another so that others will know we are Jesus’ disciples (John 13:34-35). That’s plain enough isn’t it? When the plain is plain, accept it. When the Scripture is cloudy, reference it. Textualism can be used as a theory in which the interpretation of the law is primarily based on the ordinary meaning of the legal text, or in our case, Scripture, and this is done when no consideration is given to non-textual sources. For example, we might overlook the intention of one of the laws of God because we don’t understand what specific problem that it was intended to address, so the best advice is to use caution in reading meaning into Scripture. All it takes is a little textualism.
Here is some related reading for you: How Do We Know the Bible is True? Is it Really the Word of God? 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible: English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.