When did the one-way monologue sermon first become a normal feature of church assemblies?

I have noticed that Jesus did not usually preach sermons like nearly every church does today. Possibly the ‘sermon on the mount’ is an exception.

I challenge that premise. How is it that the sermon on the mount came to make it into scripture, if the disciple relating it (Matthew) only heard it one time? Also, how do we account for the similarity to the Sermon on the Plain in Luke?

Part of the answer is that, in the days before radio, television, and now the internet, indeed, before most people were even literate, if you wanted to reach a large audience you had to travel and go to them in person. A public figure would travel from town to town, and at each stop he would give much the same speech, because it would be almost an entirely new audience each time. This was how to get your message out back then.

It is likely, then, that what we have recorded in Matthew and Luke are individual re-tellings of that same stump speech. Because they traveled with Jesus, the disciples who related these speeches would have heard them potentially hundreds of times, and were likely rehearsed on them in private (especially as they were members of the 70/72 from Luke 10).

In other words, the monologue sermon was likely exactly the pattern for teaching established by Jesus Himself.

Itpastorn have already well addressed preaching at the biblical times and in time of Luther. I will try to address the time in between.

In Antiquity, preaching (during liturgical ocasions, not in evangelist settings) was a monopoly of a bishop, the successor of the Twelve (who have ordained deacons to serve, so that apostles and episkopoi had time to preach - see Acts 6,1-6). Other preachers were allowed only to read sermons written by their bishop.

In Middle Ages, the bishop's role have somewhat changed to a political representant of the Church, so the bishops had fewer and fewer time to prepage sermons and preach. Thats why ordinary priests, especially from monastic background, have started to preach themselves. Around 800, stone ambons/pulpits were only in cathedrals (bishops' churches) and monastery churches. Recorded sermons from that times concern morale, preaching on doctrine was still a domain of bishops. The audience of regular sermons (which were in latin) were mostly monks and candidates for priesthood, laymen were taught outside liturgy and in their language - this "evangelist settings" preaching could have been quite interactive.

In High Middle Ages, sermons were more common during Holy Mass, and sermons in local languages occured. On the other hand, "learned sermons" with profound theological argumentation emerged. Most preachers at these times were priest from religious orders, who could preach on doctrine. Other priests lacked the formation to preach on anything more than basic morale. First new books of homilies were written, and homiliaries from antiquity authors (by st. Augustin, Gregor the Great etc.) were copied in big amounts.

Before 1200, anyone could preach (but in "evangelist setting" manner, not in a church). In late 12th century lay preachers gained popularity, but they were suspect of heresy, at least because lack of education (many of them didn't know that they teach something else than genuine doctrine of Catholic Church, some were deliberately preaching something different, like Kathars). A break occured when mendicant orders (dominicans or "preacher brothers" and franciscans) started to preach this way themselves, but on better theological basis. At the same time bishops started to regulate lay preaching. Fourth Lateran Council in 1215 stated that a preacher needs a licence from his bishop.

From 13th century on, wandering preachers (usually from a religious order giving necessary formation to preach well) were very popular. Ideal preacher must have been able to preach anytime, he must have traveled (no one would seem original if he stayed to long on the same place) and address different audiences (from uneducated peasants to university proffessors). While ordinary preachers (all priests were preachers these times, but they had no formal education for it) mostly read sermons prepared by someone else (with no room for interactivity), these exeptional preachers were ready for questions and other reactions.

Here we meet Luther - what itpastorn have written suit perfectly to this pattern of an elite preachers who both preaches and answer question, but doesn't overrate preaching skills of his ordinary colleagues.

To sum up, one-way monologue sermon was a norm from antiquity on, with ocasional exceptions.

I believe this format was already part of the Jewish Liturgy services that took place in the synagogue, which would have included prayer, scripture reading, and a homily. Remember that Jesus, the twelve, and most of the early Christians were Jews. Much of what we do in Christianity -- particularly in Catholicism, Eastern Orthodoxy, and the early Protestant branches -- is pretty darn Jewish.

And in fact, Jesus' ministry appears to start off in Luke 4:16-30 with a Jewish liturgy. After He reads the scripture and sits down, the author states that the crowd stares at Him intently (waiting for Him to speak). I don't think it's much of a leap to say they're waiting for a monologue (sermon).

The interactive preaching you're referring to isn't part of any worship service, bread-breaking, or religious tradition. It's just a preacher in his daily life, chatting with needy people. And I think the scriptures put this sort of interaction distinctly outside of any religious customs or structures.

ADDENDUM: The sermon, as part of a worship service, is part of a ceremony that is intended to unite a congregation in a singel act of worship. It is not, therefore, intended to teach the community so much as it is to unite, encourage, and guide the community in living The Word they have already been taught. An open dialogue in the midst of a service would distract from the purpose of focusing the congregation in a single act of worship. Hence, such dialogues simply take place outside the ceremony. And we (at least in most Catholic masses) are encouraged to seek more in depth spiritual direction and education outside the ceremony.