I've been talking about this some with ministry interns, and then a friend (a member married to a military chaplain stationed overseas) shared this quote from the eminently quotable Carl Trueman:
"If the standard level of what is done in a worship service is set at that which the newest, least informed Christian can understand, we are doomed to remain forever in spiritual infancy. As Christians, we should expect worship always to be a learning experience. That requires us not only to call ministers who are able to stretch us theologically; it also means we should fill the worship service with material that draws us on to maturity."
I largely agree with his sentiment. I do think, in a post-Christian culture, if you are blessed with a high number of unbelievers attending public worship, you are smart to preach with a heavy dose of apologetics in it, "This is the way Christians believe and live, and here's why it makes sense," feeds Christians well and is useful for overcoming intellectual objections to, and ignorance of, the Christian faith.
We need to remember the primary purpose of worship is worship --evangelistic benefit is important but secondary. WE ought to preach evangelistically, and the gospel always held forth, but, as Trueman notes, we cannot choose the "lowest common denominator" approach.
I wonder if reaching our world calls for some new thinking about how we bring people in to the community of faith. Actually, I think it requires some old thinking. The early church, seeing converts from every walk of life, high born and slave, Jew and Greek and Slav, did not change its worship, but it made the point of entry catechesis. Some have started to appropriate this idea and re-tool it for a new age (witness The New City Catechism). In some senses, it is the genius behind the Alpha and Christianity Explored courses --places where ideas can be bantered about, and the Christian faith put forward in a less authoritative atmosphere than public worship (which ought to be authoritative, by the way).
I think this is a necessary step. Adult Sunday School needs to change. It ought to be a progression of learning --from inquirers, to newborn Christians, to pressing on to Christian maturity. Again, the wheel has already been invented. Worldwide Discipleship Association has a curriculum designed to bring Christians from infancy to maturity --certainly, if not a wholesale appropriation, we could learn from and use what they have developed worldwide.
If God granted us a harvest of souls, would we know what to do with them? Maybe if we think about it in advance, he will do just that.