No matter what direction you choose to go, preach the Word to deliver the Christ!
The Sundays of the Trinity season, or the Sundays after Pentecost, are the teaching season of the Church. Unless the Sunday is exceptional with a feast or other special celebration during this period, the epistle texts in the lectionary have no intentional thematic connection with the Old Testament and Gospel readings.
So, a few pieces of general preaching advice before we get to the Sundays after Pentecost:
1: Do not try to discover a theme (it is not meant to be there!).
2: Avoid attempting to manufacture a theme. Yes, all scripture is unified in its author and its overarching plot and purpose but try not to do what an old pastor I once worked with did every Sunday he was in the pulpit, proclaiming, “The message today comes from all three texts.” This is not a poor thing to conceive. Of courses a homiletically and liturgically responsible preacher will indeed prepare by looking at the entire lectionary and put his thoughts to the ears of the hearer for that day to anticipate connections across the experience. It is, however, overly ambitious if the preacher desires to preach a text within a reasonable time frame and not simply use text(s) as a backdrop for differently motivated pulpit time.
3: This is some advice I heard as a young preacher. The best practice for congregations with long-term pastors that follow the traditional three-year lectionary is to spend the first few years preaching all the gospel texts, the next few preaching all the epistles, and the next few preaching all the Old Testament texts. This will provide almost a decade of old sermons to have at your fingertips and dive back into and mine should there be any gems worth retrieving and reviving from your younger years. There will be fewer than you think right now probably, but more than could be the case if you discipline yourself as a young preacher, take good notes, and archive well! Furthermore, a decade of responsible exegetical work (again, if you discipline yourself early and often) will serve immeasurably more in ministry than simply a weekly sermon.
Please, forgive the digression, but I come by it honestly. On the one hand I have known preachers who have over the course of their career eschewed any sort of preaching “plan” to get through the scriptures comprehensively and systematically (which the Revised Common Lectionary/three-year lectionary does). What ends up happening is they preach a handful of themes and a handful of cherry-picked texts. Generally speaking, there will be a danger here of not preaching the “whole Word.” Sometimes it may even be a symptom of a deeper laziness, and it also risks inflicting your own blind spots on your hearers, so be aware. The goal is to let the external Word (and in the case of the lectionary, walking together in the tradition and heritage of many who did and still are following these prepared texts) regulate your confrontation with the scripture, its theology, and your delivery to the Lord’s people.
On the other hand, I have also known preachers who follow the three-year series and simply avoid the more challenging texts, opting for gospels mostly and saving Old Testament and epistle texts for times when they want variety or simply an easier go than one of the “hard sayings” of our Lord. For example, feeling unsure about that Luke 16 shrewd manager parable or our Lord’s retort to the Syrophoenician woman about giving children’s food to the dogs, quickly jump to one of the others so you do not have to put in the time and effort. Exegeting texts for the sake of crafting sermons (and teaching) is itself a learning experience. If you are a young theologian (or more seasoned; it is never too late), rather than risking shortchanging yourself by picking and choosing among options here and there, commit to a plan, which could and probably should include a year (or two or three) of preaching the epistle texts of the three-year series.
Now, I feel compelled to offer just a couple more personal opinions about preaching the epistles before I get into the nitty-gritty of the Pentecost season, because there are some practices you should think about before getting into or continuing them.
I think “sermon series” frequently come off as pointless. Here, I am speaking from the perspective of a hearer in the pew, which I mostly am in this season. I do not think most people are really that engaged with series anyhow, but preachers who prefer a teaching style like them because it gives a specific focus for an extended seminar. Series generally do not honor a lectionary, and they are sometimes pretty bad when they do. I am talking about when a preacher decides to paste the patina of a four-to-six-week theme over not-necessarily-connected texts through a season of Sundays. I have seen it all: Easter season gospels as a backdrop for catechesis in prayer; Old Testament lessons to engage with prophetic texts in general; paraenetic clusters to teach virtues for a few weeks; and the like.
Having said my piece with this, recognize that choosing to exercise your freedom to “preach a series” is actually quite feasible with some epistles. Particularly in the lengthy summer and Pentecost season, you have the opportunity to dig into the greatest hits for several connected and cohesive weeks at a time. Year C gives you four weeks in Colossians, the concluding faith arc of Hebrews for a few weeks, and even seven weeks of pastorals prior to All Saints’ Day. If you really feel the yen to put together a series, and want to stay with the three-year lectionary, Pentecost epistles are the way to go.
One final note: No matter what direction you choose to go, preach the Word to deliver the Christ!
