WHAT IS EXPOSITORY PREACHING?
1. "Expository preaching" is simply preaching that which God has said in the context in which it was written.
So what does God say regarding preaching? In his letter to Timothy Paul writes: "I solemnly charge you in the presence of God and of Christ Jesus, who is to judge the living and the dead, and by His appearing and His kingdom: preach the word; be ready in season and out of season; reprove, rebuke, exhort, with great patience and instruction. For the time will come when they will not endure sound doctrine; but wanting to have their ears tickled they will accumulate for themselves teaches in accordance to their own desires, and will turn away their ears from the truth and will turn aside to myths." - II Tim. 4:1-3
What a passage "means to me" is irrelevant if it differs from that which God chose to say originally, to those whom He inspired to write it down His words. A given passage of Scripture has one and only one correct translation. It is both (original) language dependant and context dependant. That which God has said can be translated from the original language(s) such that it can be proclaimed throughout the world. It may be said in different languages and in different ways, but the core meaning always remains the same.
2. That being said, this single "correct" translation can yield numerous applications. People sitting side by side in church may hear the same sermon and yet "hear" different applications. Why? - Because they come into the service with different needs and God is working on their hearts individually. The pastor's job is not to change "his" congregation. It is simply to preach the Word of God faithfully. God is the one Who takes that single sermon and then applies it in individual hearts as He sees fit and when He sees fit.
3. The goal of expository preaching is to preach the written Word of God faithfully, in context, and in its entirety; so that God is glorified and people are brought to a saving knowledge of our Lord Jesus Christ. Though expository sermons may be evangelistic in nature at times, not every sermon is necessarily focused on "saving lost sinners". God may use it to save the lost, but expository preaching focuses on equipping believers so that they can go back into the world to proclaim the Gospel to the people they know.
So why does God choose to reveal Himself through the written Word of God - the Bible? As Al Mohler puts it "it is God whispering to us, like a father whispering to his child, so as not to scare that child in the process of correction".
What is expository preaching? - Listen to John Piper speak on the subject
Therefore, expository preaching is preaching in such a fashion so that the person preaching reveals that which God has whispered in His Word, without adding to or subtracting from that which was understood by those first hearing it.