If you preach through the entirety of the Scriptures, not every sermon is going to have Christ as the central figure. Now in the big scheme of your preaching sure He is. Like one was saying above,
One of the dangers of the redemptive-historical method is that the forest is emphasized at the expense of the trees
. If every sermon, even from the middle of Esther or some other book, is specifically about Jesus (sure in the large picture everything is about or points to Him) then the forest is emphasized at the expense of the trees and over time your congregation will suffer. Both have to be emphasized in their proper places. There are indicatives and imperatives in the Gospel message. Some texts will lend more towards indicative: this is what has happened, this is who you are; but don't forget also the imperatives that stand on the shoulders of the indicative: this is what must be done now, worship, holiness/obedience.
So asking, "Is He the subject of the verbs?" Not all the time, No and for good reason. I'm preaching here coming up 2 sermons on Rev. 12, and one sermon is focused on Satan. My sermon's subject is Satan not Jesus. Who is Satan and what does that mean for us.
Does the words Jesus or Christ have to be mentioned in every sermon, "Is Christ mentioned?" No, sometimes, especially in the OT you are talking about the Lord or God, so yes and no. If the text doesn't say Jesus or Christ, then I am not necessarily going to mention Jesus, but perhaps in an evangelistic way. If in Esther, perhaps you are going to preach on how to live as a Christian or Ruth, the focus isn't on Jesus and you don't necessarily have to mention Him, ESPECIALLY if you are preaching through a book to the same congregation.
Not every sermon is specifically about Jesus Christ. Not every sermon is about the forest (in other words), sometimes it has to be about the trees. Not all the time, but sometime.