Historical evangelical revivalism used service elements to prepare people to hear a preached message that proclaimed the Gospel.
Bringing that format, and those elements into week by week worship brings the same pressure to bear on the sermon every week to proclaim the Gospel, otherwise the worship would be missing that essential element.
This article from Ad Fontes explains how the elements of a worship service proclaim, present, and nourish people in the Gospel in a way that enables the preaching element to faithfully focus on the text succumbing to the need to import elements of Gospel theology that aren’t present in the text or its relevant application.
From the article:
a good liturgy can alleviate the “gospel-centred” burden from our preaching. Now, that’s not to say that you remove Gospel proclamation from your preaching and focus instead on difficult textual details. The Reformers would be the first to say that preaching must be preaching of the Gospel. But, in practice, being “gospel-centred” often means cramming in a short, basic Gospel summary (usually incorporating justification by faith alone) somewhere into our sermons, hoping to both convert unbelievers and remind believers to Keep The Main Thing The Main Thing. Yet this often means we violate our key evangelical commitment to expository preaching, because we are tacking something onto the text which it simply doesn’t talk about. Being “gospel-centred” often equates to being exegetically lax.
But if our liturgy always delivers The Main Thing – in its overall shape, in the confession and absolution, in a weekly Lord’s Supper – then the burden to cram a Gospel summary into our sermon on Genesis 38 is removed. You know that someone who’s just walked in the door and never heard the name of Jesus before will hear the basic Christian message during the service, whatever you say from the pulpit. And so you’re free to better engage that week’s passage on its own terms, and to uniquely proclaim the Gospel that week in those terms, which is precisely what expository preaching is all about.