Dennis E. Johnson summarizes three central emphases of Tim Keller‘s homiletic approach to illustrate how “the gospel changes everything” in “an approach to evangelistic, edificatory redemptive-historical preaching” (Him We Proclaim: Preaching Christ from All the Scriptures [Phillipsburg, NJ: P&R Publishing, 2007], 54–61):

1) What both the unbeliever and the believer need to hear in preaching is the gospel, with its implications for a life lived in confident gratitude in response to amazing grace. Christians are constantly tempted to relapse into legalistic attitudes in their pursuit of sanctification, so we never outgrow our need to hear the good news of God’s free and sovereign grace in Christ. . . .

2) The root of the unbeliever’s sin and misery is his worship (recognized or, often, unrecognized) of a false god, an idol. Likewise the believer’s frustration, resentment, lack of joy, anger, worry, fear, etc., are symptoms of lingering allegiance to various idols of the heart that persistently reassert themselves as rivals with Jesus for our trust, devotion, and service. . . .

3) The preacher and his congregation assume the presence of unbelievers in their midst, people to whom the “language of Zion” is a foreign tongue and to whom biblical truths (including the very concept of absolute truth) are alien. Preaching must take account of the fact that the truths of the gospel are counter-intuitive to the unregenerate mind, and this reality is becoming more overt as western culture abandons even the shell of a biblical worldview. Therefore, preaching must incorporate apologetics—“sidebars” addressed to unbelievers where the preacher frankly acknowledges the alienness of the gospel to prevailing cultural assumptions but also respectfully challenges non-Christians to recognize the coherence of biblical truth and its superior adequacy to address the dilemmas of human life and thought. . . .

[T]he preacher himself must be the cross-cultural traveler and translator, bringing the Bible’s alien message into the indigenous language and thought-forms of those to whom God has sent him.

Related:

1. Preaching Christ in a Postmodern World
2. Preaching to the Heart
3. Examples:
   1. The Reason for God.
   2. The Prodigal God. Cf. my review.
   3. Counterfeit Gods. Cf. my review.
4. Mike Bullmore’s 2008 Rom Lectures: “The Heart of Preaching and the Preacher’s Heart”