Here is a key to great earnestness in preaching. If you really believe that "those who endure to the end will be saved" (Mark 13:13), and that not only the first act of faith but all subsequent acts of persevering faith are sustained by the Spirit through the Word of God, then virtually every sermon is a "salvation sermon" and the souls of the saints are being saved every Sunday. There is not an earnest sermon for evangelism when the souls of the lost are at stake, and then a less serious and less critical message for the saints to simply add a few stars in their crown. Rather every sermon is crucial and critical in sustaining the faith of the saints and so bringing them safely to glory.