Expository or topical teaching?
The norm in our churches should be “expository” teaching through books of the Bible. That is, teaching paragraph by paragraph, chapter by chapter, through an entire book of the Bible, and then starting anew elsewhere. Of course, we would be wise not to bite off more than we can chew in a single teaching, and should not to go too slowly through a single book either. And the genre of the book certainly will influence the pace.
The purpose of this recommendation is that we might be able to testify as Paul did before the Ephesian elders.
Therefore I testify to you this day that I am innocent of the blood of all, for I did not shrink from declaring to you the whole counsel of God.
Acts 20:26-27
There are two reasons why expository teaching is preferred toward this end, over and above topical teaching.
Expository teaching allows God, as author of his Word, to set the topical agenda. True, we may know many issues in the lives of our hearers, but we don't know all of them. In fact, they do not even know all they need to hear—but God does.
If we do not teach through books, we will never get to things that God deems important. God has given us all different personalities and experiences, but that does not mean he wants this to be what drives the focus of our teaching.
That being said, certainly different contexts require different considerations. Are you the regular (weekly) teacher of a Bible study or preacher in the church, or do you just teach on occasion? If the latter, then expository teaching through a book of the Bible may not even be an option. And certainly there are occasions when regular teachers/preachers would do well to take a break in order to address an important issue in the life of the church. The idea here is not to form rules, but to consider wisdom in how we faithfully teach the Word.
Teach both testaments
God clearly did not want to reveal himself and his plan to us in a flat, simplistic form of literature. While gospel tracts and systematic theologies are valuable, the Bible is neither of these. Thus God clearly is not calling gospel teachers to merely teach the passages which communicate the gospel most simply and clearly. Neither is he calling us to leave the Old Testament behind.
Clarity is really important, and certainly everything has become much clearer with the coming of Christ. But glory is also really important. We were made to worship, and seeing the progressive revelation of God and his sovereign workings in Israel, unfolds for us amazing vistas of that glory. And this is not to mention the historical roots, examples, songs and practical wisdom we find exclusively in the Old Testament.
It is for this reason that nearly half of your assignments instruct you to choose a text from the Old Testament.
Read the text
Another point of consideration is whether to read the text in full that you are teaching. This is not much of a question when dealing with short passages, but what about narrative passages, lengthy prophesies and even genealogies?
Apart from one caveat, we encourage you to read the text in full. The exception would be if you are teaching on a text which would properly be defined as reference material, such as genealogies or architectural instructions or descriptions. Such passages are also the word of God and therefore also infinitely important, but their importance may be as a resource to check details more than as a manuscript to read through. Ask yourself, “Is this a text in a genre that was meant to be read through?” If so, why would we not do so as a part of our teaching?
But the passage is quite long and thus I might lose my hearers. The scriptures are not boring, and so I would suggest that the issue is rather that you have not meditated on the text enough so as to read it well. Or perhaps you need to choose a translation that is more understandable, or break-up your reading of the text with your teaching interjected throughout? Bottom line, the best thing you have to say is the scripture text you will read.
Consider this example below from Sam Crabtree. Listen to at least the first four and a half minutes, and more if you like.
Until I come, devote yourself to the public reading of Scripture, to exhortation, to teaching.
1 Timothy 4:13