On one level it is a feeling that can come for any reason. A little moment of doubt. An unexpected event, or listener, or conversation, or comment . . . and suddenly the temptation is there to give up on the planned message. Some may have this feeling every time they preach. Others may never get it at all. But is there a genuine reason to abort the message and switch to something else?
In his excellent chapter on Charles Simeon in Preach the Word, J.I. Packer states the following:
Simeon would go on to remind us that expository preaching should be textual in character. The preacher’s task, according to him, was not imposition, giving texts meaning the do not bear; nor was it juxtaposition, using texts merely as pegs on which to hand general reflections imported from elsewhere (“preachments of this kind are extremely disgustful”); it was, precisely, exposition, bringing out of teh texts what God had put in them “I never preach,” said Simeon, “unless I feel satisfied that I have the mind of God as regards the sense of the passage.” (Preach the Word, 147)
There may be more than one reason to abort a sermon, but this one alone is worth pondering. If we are not satisfied that we have the mind of God as regards the sense of a passage . . . we should not preach it! Better to preach an unprepared sermon at a moment’s notice on a text we do understand, than to preach a prepared sermon built on shaking exegesis. If you really don’t get, don’t preach it. Abort sermon!