A friend recently summed up the purpose of the funeral sermon with this short sample of a most direct (and, of course, undeliverable) sermon.
It is important at this funeral Mass to pray for N., who is in the box (pointing to the casket); that is very important; it is essential, in fact.
But the greatest reason I am preaching to you is to remind you that we are all going to end up in the box!
Prepare your soul for death with a holy life.
The 1962 Burial Service Rite has a prayer with the same idea somewhat more eloquently expressed in the PRAYERS FOR THE BYSTANDERS AT THE GRAVE.
Grant, O Lord, we beseech Thee, that whilst we lament the departure of our brother/sister, Thy servant out of this life, we may bear in mind that we are most certainly to follow him/her. Give us grace to make ready for that last hour by a devout and holy life, and protect us against a sudden and unprovided death. Teach us how to watch and pray that when Thy summons comes, we may go forth to meet the Bridegroom and enter with Him into life everlasting. Through Christ our Lord. Amen.