Howard Hendricks wrote The Seven Laws of the Teacher, in which he refers to an English bishop who said, “You know, wherever the apostle Paul went, they had a riot or a revival. Wherever I go, they serve tea.” (p165.)
I am sure all of us have experienced the soaring anticipation of a sermon, as well as the crashing experience of being crushed by non-response on the day. Someone famous (probably Spurgeon, but I can’t remember), said that we should not over-estimate what can be achieved in a single sermon, but also never under-estimate what will happen through several years of faithful biblical preaching.
Somehow we have to hold two tensions together. On the one hand, we know that God can and does work in a single sermon to bring about radical life change. On the other hand, we know that often the change God is working into the lives of a congregation are imperceptible and we will regularly be tempted to despair.
When you see genuine response and transformation, document it. Keep that document somewhere safe, but easily accessible. There will be lots of weeks where you will value the reminder.