Sermon on the Plain Counterpart

[CyrilSebastian]

In the Saint Joseph Edition of The New American Bible, a footnote states:
Luke’s “Sermon on the Plain” (Luke 6, 20-49) is the counterpart to Matthew’s “Sermon on the Mount” (Matthew 5, 1 - 7, 27).

How can a writing of Luke’s be the counterpart to a writing of Matthew’s?

 

[sirach2v4]

The three “synoptic” (one eye) gospels repeat a lot of material, although it may be presented in slightly different fashion. One idea that harmonizes this, is that Jesus repeated some of his teaching at different times. For example, it is suggested that all the beatitudes that are listed together in Mt’s gospel may have been taught at different times, but been written together in Mt’s gospel.