God: "I looked for someone to take a stand for me, and stand in the gap" (Ezekiel 22:30)
The sermon which does not lead to Christ, or of which Jesus Christ is not the top and the bottom, is a sort of sermon that will make the devils in hell laugh, but make the angels of God weep.
The Word of God alone is to be preached, in its perfection and inner consistency. Scripture is the exclusive subject of preaching, the only field in which the preacher is to labour.