Three reasons to draw in other texts
In a previous lesson, we discussed the necessity of knowing the message of the Bible so as to know the larger context of the passage. Along these lines, let us also consider when and how to include cross references in our teaching on a text.
Establishing context
First, drawing in other texts to your teaching is helpful for establishing the context. It is always necessary for us to know the biblical context well as we form our teaching, and oftentimes there is great worth in explicitly developing that context for our hearers. Sometimes this will be be done through a description of the context on our part, and other times our hearers will be most helped through the quoting of one or more texts which establish that context.
Alistair Begg, in preaching on 2 Timothy 3:1-9, demonstrates a sort of hybrid of these two. He does not read a quotation of Acts 20, but does recall the content there with a summarizing paraphrase in order to establish the context of 2 Timothy.
Supporting your interpretation
Secondly, there are times to draw in other texts of the Bible in order to backup and reinforce what we are interpreting the central text of our study to be saying. After all, if we are getting our interpretation right, we should expect to find the truths we are seeing also affirmed elsewhere in Scripture. Thus, drawing in those other texts can be helpful for reassuring our hearers that we are indeed reading the passage correctly, and also helpful for illuminating the point being made through seeing it expressed in a different way, in a different part of the Bible.
From the same sermon presented above, note here how Alistair Begg argues a point from the text itself and then goes on to reinforce that interpretation from two other texts.
However, in saying that “there are times” to support our teaching by drawing in other texts, we are being intentionally non-absolute. For biblical observation demonstrates that wisdom is needed to know when to include texts for the sake of proving our teaching. That is, oftentimes we find the Bible itself doing this very thing when it quotes previous revelation and reasons through those texts to establish a point. But not always. Sometimes the author simply declares what is true. That is not to say that the biblical authors in these instances could not have proven their points biblically. Rather, we are saying that discernment is needed, given your audience and the occasion, to know when to do one and when to do the other. (Note, for example, these passages from Colossians and Ephesians, one which includes biblical proof, and the other which does not.)
Children, obey your parents in everything, for this pleases the Lord.
Colossians 3:20
Children, obey your parents in the Lord, for this is right. ‘Honor your father and mother’ (this is the first commandment with a promise), ‘that it may go well with you and that you may live long in the land.’
Ephesians 6:1-3 (quoting Exodus 20:12)
It comes down to this. The essence of biblical teaching is declaring the truths found in the Bible. This is always a component of faithfully teaching the scriptures. Backing up that declaration with the persuasive unpacking of a variety of texts is wonderful, and often important to include, but not always. Our teaching must always declare the truth of the text, and sometimes prove it. Or stated from the other direction, we always need to have the proof, but do not always need to present it.
Supporting the implications
Finally, at times we need to draw in other texts in order to support what we believe the central teaching text to be implying—whether that be a theological truth or practical application. This is distinct from the second reason since here we are not talking about the explicit teaching of the text, but rather the truths it leads us to understand and lives it leads us to live. Narrative texts, for example, will often leave us needing to draw out the lesson that is not explicitly stated in the text (but is no less there). We certainly ought to teach such implications, and usually will do so best by drawing in other texts to support our conclusions.
Let's take one more look at Alistair Begg's sermon on 2 Timothy 3:1-9. In this clip, he clarifies both what is not the implication and what is the implication of the text by turning to 1 Corinthians 5.
Three dangers to drawing in other texts
However, there are also pitfalls to drawing in other texts to our teaching on a passage. This may surprise you. After all, how could you go wrong in teaching the Bible by bringing in more of the Bible? And yet you can, as we will see in considering the three dangers enumerated below.
Teaching your favorite message
First off, drawing in other texts at times can be a way of teaching your favorite message on the text's topic over and above the message of the text. The fact that I have taught biblical truth on the topic of my main passage, does not mean I have taught my passage—even if I do weave in a dozen different texts!
Do not love the world or the things in the world. If anyone loves the world, the love of the Father is not in him.
1 John 2:15
If this is my base text, the central lesson of my teaching should not be that we are called to live in the world but not be of the world. That is the message of John 17:15-19. I might love that passage, but here God has a different (though related) message on the topic of the world. John 17:15-19 is relevant and you may very well want to make reference to it, but not in a way that would take away from the central message of the text at hand—namely, that the love of God in a person causes him to love God far above this world.
Teaching systematic theology
Similarly, I have not taught a text if my lesson is essentially a systematic theology on the topic at hand. Now there is most certainly a place for systematic theology, as the book of Romans demonstrates! But this is not the same as teaching a particular passage. The primary danger is that I would never let many parts of the Bible simply speak for themselves. That is, passages which make points that go beyond the systematic theology summary on the topic, passages which demonstrate God's wisdom through his progressive revelation and the unfolding of his salvific plan, and passages whose purpose is to make our hearts feel the weight of biblical doctrines—passages like these will never be heard if all we ever do is systematic theology.
Teaching what the text does not mean
Thirdly, teachers sometimes draw in other texts to establish what the central teaching passage does not mean. This can be helpful, but has gone too far if either (1) you never talk about what the central text does mean, or (2) if you make what it does not mean the central point in your teaching.
For example, you might teach James 2 and spend a little time showing that James is not teaching salvation by works, making your point in part by referencing Ephesians 2. But we must remember that while Ephesians 2 can help us correctly interpret James 2, it does not get to disqualify or negate it. Thus, you cannot simply establish what James 2 does not mean; your main purpose must be to teach what it does mean.
The goal is to teach the message of the text at hand. Other texts should be drawn into our teaching so far as they serve this aim, and never to the detriment of it.