But there has to be more. Prior to collectively witnessing to God's coming kingdom, Christians need to be instructed in the faith, or better, they need to be formed into how to live faithfully. In other words, along with witnessing to God's coming kingdom, one of the church's purposes is Christian formation, and, unsurprisingly, this occurs primarily in worship (although education should play a key role too). As the theologian James K. A. Smith notes, "Liturgies or worship practices are rituals of ultimate concern that are formative of our identity--they both reflect what matters to us and shape what matters to us" (Desiring the Kingdom, p. 93). Finally, and perhaps most importantly, worship must provide an opportunity for individuals to encounter God or the divine. It needs to be a setting in which people feel they can come in contact with the sacred.
If all this is correct, then in addition to encountering the sacred, the purpose for worship is at least three-fold. First, it must seek to evoke a sense of the sacred. It has to differ from a meeting of the American Civil Liberties Union or the Family Research Council. It needs to be distinctive. In fact, there is considerable evidence that there is a positive association between distinctive faith communities and the strength of those communities ("Why Strict Churches Are Strong").
Second, it must provide a living witness to God's coming kingdom. When "outsiders" look at those gathered for worship, it should provide them with a "glimpse" of God's kingdom. For instance, reflecting on a recent Christmas Eve service I attended ("The Wideness of God's Kingdom") I couldn't shake the feeling that
everyone was there: old and young, rich and poor, unlettered and cultured, gay and straight, infirm and healthy (there might've even been Dodger and Seahawks fans there). And in the midst of singing classic Christmas hymns, I couldn't help think that I was catching a glimpse of God's Kingdom.
Third, worship must also help people learn what it means to embody the Christian faith. It is here that preaching, music, and the celebration of communion play key roles. Preaching is central because it helps articulate the nature of God's kingdom; it proclaims the risen Christ among us. Communion is central because of its associated images of a open table where all are welcome and no one is turned away ("What Are Christians to Make of Communion?"):
Communion isn't simply a remembrance of the last meal Jesus shared with his disciples, but rather it recalls all of the images associated with an open table, whether they are from ancient Israel, Jesus' table fellowship with his disciples, or the numerous parables he told about God's heavenly banquet.
And then there is the music. I can't remember who said it, but someone once remarked that people "learn" their theology more through the hymns and songs that they sing than the sermons they hear. This may be a bit of an exaggeration, but it is almost certain that music plays a key role in the formation of one's faith, which is why churches should pay close attention to the theological content of the songs they sing.
Needless to say, well-meaning Christians can disagree as to the nature of God's kingdom (I daresay that some probably find my vision of the kingdom too inclusive, while others find it too eschatological). Thus, how people embody God's kingdom will differ from time-to-time and place-to-place. That, however, is a topic for another day.