Matthean discourse finales.

Five instances of the same phrase after a dominical discourse.

Exactly five times in his gospel, Matthew wraps up a discourse by Jesus with the same clause: Και εγενετο οτε ετελεσεν ο Ιησους.... The five discourses are:

The sermon on the mount: Matthew 5.1-7.29.
The mission instructions: Matthew 10.1-11.1.
The parables at seaside: Matthew 13.1-53.
The last discourse of the Galilean ministry: Matthew 18.1-19.2.
The Olivet discourse: Matthew 24.1-26.2, perhaps also including 23.1-39.

Stylistically, the finales of these five discourses can be picked out easily across the gospel, since they are the only instances in Matthew of εγενετο followed by a finite verb (5-2-22+0), which is a predominantly Lucan construction.

Sometimes the ensuing clause parallels material in another synoptic gospel. This material is noted below. Once the clause itself is paralleled in Luke. This Lucan clause, too, is included, though not one word of it is reflected verbatim in Matthew.

The five finales are as follows:

The sermon on the mount ends with Matthew 7.28: Και εγενετο οτε ετελεσεν ο Ιησους τους λογους τουτους εξεπλησσοντο οι οχλοι επι τη διδαχη αυτου (and it happened that when Jesus finished these words the crowds were amazed at his teaching). Mark 1.22a has και εξεπλησσοντο επι τη διδαχη αυτου (and they were amazed at his teaching), and the next Marcan lines parallel the next Matthean lines, as well. Luke 7.1: Επειδη επληρωσεν παντα τα ρηματα αυτου εις τας ακοας του λαου, εισηλθεν εις Καφαρναουμ (when he fulfilled all his words in the hearing of the people, he went into Capernaum). And Luke 4.32a has και εξεπλησσοντο επι τη διδαχη αυτου (and they were amazed at his teaching).
The mission discourse ends with Matthew 11.1: Και εγενετο οτε ετελεσεν ο Ιησους διατασσων τοις δωδεκα μαθηταις αυτου μετεβη εκειθεν του διδασκειν και κηρυσσειν εν ταις πολεσιν αυτων (and it happened that when Jesus finished ordering his twelve disciples he departed thence to teach and to preach in their cities).
The parables by the sea end with Matthew 13.53: Και εγενετο οτε ετελεσεν ο Ιησους τας παραβολας ταυτας μετηρεν εκειθεν (and it happened that when Jesus finished these parables he removed himself thence).
The discourse on scandals ends with Matthew 19.1-2: Και εγενετο οτε ετελεσεν ο Ιησους τους λογους τουτους μετηρεν απο της Γαλιλαιας και ηλθεν εις τα ορια της Ιουδαιας περαν του Ιορδανου (and it happened that when Jesus finished these words he removed himself from Galilee and came unto the borders of Judea across the Jordan). Mark 10.1 has και εκειθεν αναστας ερχεται εις τα ορια της Ιουδαιας και περαν του Ιορδανου (and standing up thence he comes unto the borders of Judea and across the Jordan).
The Olivet discourse ends with Matthew 26.1-2: Και εγενετο οτε ετελεσεν ο Ιησους παντας τους λογους τουτους ειπεν τοις μαθηταις αυτου· Οιδατε οτι μετα δυο ημερας το πασχα γινεται, και ο υιος του ανθρωπου παραδιδοται εις το σταυρωθηναι (and it happened that when Jesus finished all these words he said to his disciples: You know that after two days the Passover is coming, and the son of man is being delivered up to be crucified). Mark 14.1a has ην δε το πασχα και τα αζυμα μετα δυο ημερας (but it was the Passover and [feast of] Unleavened Bread after two days). Luke 22.1 has ηγγιζεν δε η εορτη των αζυμων η λεγομενη πασχα (but the feast of Unleavened Bread was at hand, which was called the Passover).

It is worth noting that Matthew seems to have had six discourses at his disposal, not five, yet still chose to apply his formula only five times. The discourse against the scribes and Pharisees in Matthew 23.1-39, separated from the Olivet discourse by the scene change (from the temple to Olivet) in 24.1-3, is clearly its own unit, yet does not receive its own finale formula. Matthew appears to be eliding it with Olivet itself; perhaps that is why he has omitted the incident of the widow and the mites (Mark 12.41-44 = Luke 21.1-4), which in Mark and Luke further separates the words against the scribes (Mark 12.38-40 = Luke 20.45-47) from the Olivet discourse.

Why is Matthew so bent on setting five (and only five) discourses before his readership? Is it in imitation of the five books of Moses, the Pentateuch? Is it because he feels that five is the most appropriate number for discourse material (confer the five books of Papias dedicated to interpreting the λογια of the Lord)? Is there some other reason?

It seems odd to me that Matthew 7.28a and Luke 7.1a...:

Και εγενετο οτε ετελεσεν ο Ιησους τους λογους τουτους... οι οχλοι....

And it happened that when Jesus finished these words... the crowds....

Επειδη επληρωσεν παντα τα ρηματα αυτου εις τας ακοας του λαου....

When he fulfilled all his words in the hearing of the people....

...should mean virtually the same thing and come at exactly the same point in the narrative (the close of the sermon on the mount or plain), yet should happen to use none of the same Greek words. Is this coincidental or by design? Note also that the great sermon takes place in Matthew 5.1 after Jesus has gone up onto the mountain (εις το ορος), but in Luke 6.17 after Jesus has come down the mountain to stand upon a level place (επι τοπου πεδινου). Again, is this reversal coincidental or by design?

Scan this vocabulary list for Matthew 7.28a = Luke 7.1a (parenthetical word counts explained on my page about synoptic vocabulary):

οχλος, crowd, singular or plural (50-38-41+22); οχλοι, plural only (31-1-16+7)
λαος, people (14-2-36+48)

οτε, when (12-12-12+10)
επειδη, emphatic when (0-0-2+3); επει, when (3-1-1+0)

τελεω, finish (7-0-4+1)
πληροω, fulfill (16-2-9+16)

λογος, word (33-24-32+65)
ρημα, word (5-2-19+14)

εγενετο, it happened, followed by a finite verb (5-2-22+0)

Notice the synonym pairs. In each case Matthew has employed the first, Luke the second. Furthermore, εγενετο is characteristically Lucan when followed by a finite verb; yet in this case he chooses a different construction.