From Edmund Clowney’s Preaching Christ from All of Scripture (Crossway, 2003), 55:

One one occasion I had tea with Martin Lloyd-Jones in Ealing, London, and decided to ask him a question that concerned me.  “Dr. Lloyd-Jones,” I said, “how can I tell whether I am preaching in the energy of the flesh or in the power of the Spirit?”

“That is very easy,” Lloyd-Jones replied, as I shriveled. “If you are preaching in the energy of the flesh, you will feel exalted and lifted up.  If you are preaching in the power of the Spirit, you will feel awe and humility.”