Trying to penetrate deep into the mysteries of preaching, including reflection on most recent sermons I have heard or preached myself, I remain convinced that being able to sum up the message of the sermon in one sentence is the key to great preaching. Allied with 'one sentence' as a methodological tool to preach better sermons, I remind myself that 'simplicity' as an aim for each sermon is vital to the most effective preaching (in the sense that effective preaching, at the least, communicates a message which is remembered when the sermon is over). Simplicity includes avoiding sidetracks (interesting though they may be) and side passages (good and true though they may be), as well as returning again and again to the message being delivered.
It is possible to deliver a non-simple, multiple messages sermon which people appreciate in a variety of ways. One of the several messages 'hits home'. One of the stories told is deliciously entertaining and memorable. The deliverer may be blessed with a tone and timbre of voice which means that just about anything they say has the effect of making the congregation feel good about life. These things are not irrelevant or unimportant to congregational life!
But, in the long-term, preachers may want to be more effective than 'thankfully something I said seemed to hit home to one or two' or 'I got some nice feedback about the sermon being very nice.' And congregations, to mature in Christ, need to be taught well, accumulating depth and breadth in knowledge of God's love for them in Jesus Christ, and Jesus Christ's work in them through the Holy Spirit. Simple, clear messages, week by week, over time, will be the most satisfying preaching for both preacher and hearers.
So, our challenge as preachers: sharpen up. One sentence summary of what we say? Yes! Simplicity of overall content? Yes, please!