1. Consecutive expository preaching safeguards God’s agenda against being hijacked by ours.
“When we do topical preaching we (as it were) hold the microphone in front of God and ask him the questions of our choice. We hold the microphone there just long enough to hear his answers, and then we take it away. We do not want to take the risk of letting him have the microphone; after all, he might want to tell us all sorts of things we may not want to hear. To do consecutive expository preaching gives God the microphone. We hand it over to him and we listen while God tells us what he wants us to hear. He sets the agenda for our teaching and learning.”

2. Consecutive expository preaching makes it harder for us to abuse the Bible by reading it out of context.
“One of the great blessings of a consecutive expository series is that we may take our hearers to the book we are studying, get them firmly grounded in it, and then quietly walk through it. We relate the different parts of the book to one another, so as to build up a far clearer and more accurate understanding of the message of the book as a whole, and each part within the whole.”

3. Consecutive expository preaching dilutes the selectivity of the preacher.
“My heart sinks when I am asked to preach a topical sermon. Someone writes and says, “Please will you preach on the topic of Christian assurance?” Help! What must I do? I ransack my mental map of the bible trying to forage from it anything that might be relevant. I only have limited time, so I cannot systematically read the Bible through from end to end. So what happens? I pick the bits of the Bible that I happen to know and love that might bear on this subject. And I try to put them in some coherent order and the give the talk. I may also enlist some help from reference books.”
“But when I tackle a consecutive exposition, I know what I have to do. Whether I like it or not, whether I am familiar with it or not, I know what I must read and re-read and pray and work and worry away at this week’s passage, like a dog at a bone, seeking to preach what this passage says and not what I happen to want to preach about.”

4. Consecutive expository preaching keeps the content of the sermon fresh and surprising.
“There are some preachers for whom you know in advance what they are going to say. If their Bible passage seems to be at least vaguely about prayer, you will get their standard prayer talk.”
“The gospel is richer and fuller than those truncated versions. Every passage in the Bible is there because it contributes something unique to God’s revelation. And when a preacher asks himself, “What does this passage contribute? Why is this truth told in this way to these hearers?” then there is a sense of healthy surprise and freshness in the preaching. It is always the same gospel, but never exactly the same sermon.”

5. Consecutive expository preaching makes for variety in the style of the sermon.
“Our preaching ought to take not just its content but also its tone and style from the passage. We ought not to preach Job in the same manner as we preach Romans. And if as ministers we are taking the tone and style from our different Bible books, then there will be in the style, manner and tone of our sermons a refreshing variety. I realize that many of us struggle with this, and our sermons do tend to revert to a default style; but consecutive expository ministry can help to free us from this.”

6. Consecutive expository preaching models good nourishing Bible reading for the ordinary Christian.
“Consecutive exposition says to the ordinary Christian: you too can take Philippians and read quietly through it day by day. You can take Philippians as a project for your personal times of Bible reading and prayer. Live in Philippians for a while. Read it all, and then read it bit by bit, connecting it up. This is a model for Bible reading that will nourish and sustain. Good topical preaching may give a Christian a fish, but good expository ministry will teach him how to fish.”

7. Consecutive expository preaching helps us preach the whole Christ from the whole of Scripture.
“Part of what brings depth to Christian discipleship is a growing awareness of who Jesus Christ is and what he means so that the word “Jesus” really does connect to the person Jesus. The only access we have to the authentic Jesus is from the whole Bible, which is the Father’s testimony given by the Spirit to the Son. It follows that we may expect to grow in our knowledge of Jesus as we are taught the whole Bible. Christians who are only ever exposed to part of the Bible are only ever exposed to a truncated Jesus. Our job as preachers is so to proclaim Christ that we may present people mature in him (Colossians 1:28-29).

Adapted from the appendix of Christopher Ash’s book The Priority of Preaching