Prepaing for Worship By Asking "What is the Aim of Our Form of Worship?"
The Presbyterian answer to this query is essentially: "our goal is to have radically biblical worship, worship that is uniquely directed by God's word, so that God is clearly in charge of both the form and substance of our worship of him.
Radically Biblical Worship
For our worship to be biblical in all its aspects means, among other things, (1) that its content, parts and corporateness are all positively in accord with Scripture; (2) that it is simultaneously a communal response of gratitude for grace, an expression of passion for God, the fulfillment of what we were made and redeemed for, a joyful engagement in a delightful obedience, as Scripture teaches; (3) that it is a corporate Christ-provided, Spirit-enabled encounter with the almighty, loving and righteous Father, and thus always has in view the Triune God, again in accord with the Bible's teaching; and (4) that it aims for and is an expression of God's own glory, and contemplates the consummation of the eternal covenant in the church triumphant's everlasting union and communion with God.
Determining that the Bible will guide our worship, helps the church ensure that the elements of worship (like singing, praying, reading Scripture, preaching, administering the sacraments, making solemn vows, confessing the faith and giving offerings) are unequivocally and positively grounded in Scripture, and that the forms of worship (how you go about singing, praying, reading Scripture, preaching, administering the sacraments) are in accord with Scripture and serve the elements they are intended to help convey, and that the circumstances of worship (incidentals like whether you sit in pews or chairs or stand, whether you meet in a church building or a storefront, what time you meet, how long you meet, etc.), are maximally helpful in assisting us to do what the Bible calls us to do in worship.
Why the manner of congregational worship is important
Presbyterians have not been concerned with forms and circumstances so much for their own sake as much as for the sake of the elements and substance of worship, and for the sake of the object and aim of worship. The Reformers (from whom Presbyterians have learned much about Scripture) understood two things often lost on moderns. First, they understood that the liturgy (the set forms of corporate worship), media, instruments and vehicles of worship are never neutral, and so exceeding care must be given to the "law of unintended consequences." Often the medium overwhelms and changes the message. For example, if you sing "Amazing Grace" to the tune of "Gilligan's Island" (the meter works, but the tune doesn't - a light, quasi-sea-shanty, with comedic associations, coupled with gravely serious words) it changes the whole tone of what one is doing in singing that text, and easily becomes a sacrilege. Second, they knew that the purpose of the elements and forms and circumstances of corporate worship is to assure that you are actually doing worship as it is defined by the God of Scripture, that you are worshiping the God of Scripture and that your aim in worshiping Him is the aim set forth in Scripture.
So Presbyterians care about how we worship not because we think that liturgy (the order of service) is prescribed, mystical or sacramental, but precisely so that the liturgy can get out of the way of the gathered church's communion with the living God. The function of the order of service is not to draw attention to itself but to aid the soul's communion with God in the gathered company of the saints by serving to convey the word of God to and from God, from and to His people. C.S. Lewis puts it this way: "As long as you notice, and have to count, the steps, you are not yet dancing but only learning to dance. A good shoe is a shoe you don't have to notice. Good reading becomes possible when you need not consciously think about eyes, or light, or print, or spelling. The perfect church service would be one we were almost unaware of; our attention would have been on God" (from Letters to Malcolm: Chiefly on Prayer). This is why the great Baptist preacher Geoffrey Thomas can say: "In true worship men have little thought of the means of worship; their thoughts are upon God. True worship is characterized by self-effacement and is lacking in any self-consciousness." That is, in biblical worship we so focus upon God Himself and are so intent to acknowledge His inherent and unique worthiness that we are transfixed by Him, and thus worship is not about what we want or like (nor do His appointed means divert our eyes from Him), but rather it is about meeting with God and delighting in Him. Praise decentralizes self.
Worship, Culture and Reverence
By the way, Presbyterians do not have the same interest in cultural accommodation as many modern evangelical worship theorists do. We are against culture-derived worship, and are more concerned to implement to principles of Scripture in our specific culture (and even to emulate the best of the Bible-inspired cultures of Scripture), than we are to reclaim current cultural forms for Christian use. This is precisely one of the areas productive of the greatest controversy in our own age. Many pastors and churches think that, in order to reach people, you must use the church's worship "style" to position the church for evangelism. Hence, pop-contemporary forms or the distinctive ethnic forms of a particular sub-culture are employed in order to reach an audience that likes that particular "style." This is exceedingly dangerous and turns the focus of corporate worship on its head, and opens the door to encouraging participants to view themselves as consumers rather than as worshipers. This is a significant problem in our consumer-oriented context.
And we Presbyterians believe that worship ought to be reverent. If worship is meeting with God, how could it be otherwise? It is precisely the reverence and awe of the greatness of God that should characterize worship at its best. We agree with Hughes Oliphant Old who says "The greatest single contribution which the Reformed liturgical heritage can make to contemporary American Protestantism is its sense of the majesty and sovereignty of God, its sense of reverence, of simple dignity, its conviction that worship must above all serve the praise of God." That's why we aim for a worship service that is Scriptural, simple, Spiritual, historic, heartfelt, majestic and reverent.