We have seen that in the New Testament churches the growth into spiritual maturity of both individuals and communities was achieved by a variety of means, which did not include the regular sermon. Indeed, the experience of the churches and current knowledge about the learning process suggest that regular use of the sermon tends to have harmful consequences. It frequently fails to instruct; it deskills; it foster an unhealthy dependence on the clergy. In these ways the regular sermon not only fails to promote spiritual growth but also intensifies the impoverishment of Christian life which characterizes large areas of the church today.
The regular sermon does not, of course, stand alone as the one great corrupter of Christian faith and life. It is embedded in a complex organizational structure which is far removed from biblical patterns and which also inhibits Christian growth to maturity. The sad irony is that many preachers want to see their congregations grow in knowledge and love. Many take a great deal of trouble over preparing their sermons. Yet the teaching method they have chosen to use is, in practice, working with other factors to frustrate their hopes.—To Preach or Not to Preach?, page 115
All of the statements above are his summary of what he has laid out in the preceding 50 plus pages, with extensive footnotes. If you disagree with his conclusions, you will have to get the book (it's out of print) and read it to see if you can negate the arguments behind his conclusions summarized above.