The sermon should ordinarily be based on the Gospel for the day, at least in part, except that on Feast Days it is assumed that the theme of the feast could have a greater prominence. On Sundays in particular, the sermon should center on the Gospel reading. It should, as Piepkorn puts it, be "strong in the power of the Gospel to move men, to give them the power to believe and to do those things which the total liturgical action of worship has been setting before them" (19).
My variation: As the congregation ought to expect that the sermon will be based on the Gospel, it is not necessary for the congregation to rise when the celebrant enters the pulpit, nor does he need to read any additional Scripture text prior to preaching. For the sermon, the preacher simply opens with an invocation of Father, Son, and Holy Ghost (with accompanying threefold thumbnail sign of the cross upon his forehead, lips, and breast), or some suitable substitute, whereupon the congregation will respond, Amen, and he begins to preach. At the conclusion of his sermon, if he chooses to repeat the Trinitarian invocation, the congregation will again respond with Amen.