http://apologeticspress.org/AllegedDiscrepancies.aspx?article=800&b=Matthew
by Eric Lyons, M.Min.
First of all, for these passages to be contradictory one must assume the two sermons were delivered at the same place and at the same time. But, as H. Leo Boles stated in his commentary on Luke, this sermon “may have been repeated a number of times and Luke gives a record of the sermon which was repeated at some later time than the record given by Matthew” (1940, p. 134). It is more than possible that Jesus repeated His teachings on various occasions. He easily could have preached the beatitudes in Capernaum as well as in Cana. He could have taught the model prayer in both Bethany and Bethsaida. Who are we to say that Jesus preached the principles and commands found in Matthew 5-7 only once? There are some men today who travel to a different city nearly every week preaching the same sermons—and do so effectively. Could Jesus not have done something similar?
A more likely solution to this geographical “problem” is simply to understand that Matthew and Luke were referring to the same sermon, and that Jesus was preaching it while being both on a mountain and on a “plain” (KJV) at the same time. The word “plain” (tópou pedinoú) simply means “ level place” (Wycliffe, 1985), and is translated thusly in nearly all modern versions of the Bible. Since a mountain can have level places on it, no one can assert logically that Matthew 5:1 and Luke 6:17 are contradictory. I have been to the top of a mountain in Anchorage, Alaska, that is so level it is known as “Flattop Mountain.” To say Jesus stood on a level place on a mountain is no oxymoron.
REFERENCES
Boles, H. Leo (1940), A Commentary on the Gospel According to Luke (Nashville, TN: Gospel Advocate).
Wycliffe Bible Commentary (1985), Electronic Database: Biblesoft.