Problem: Luke says that Jesus “stood on a level place” to preach. But Matthew recorded that “when He was seated … He opened His mouth and taught them” (Matt. 5:1–2).
Solution: These references may be of slightly different times during the same event. One possibility is that Matthew’s reference is to the beginning of the event when “His disciples came to Him … and [He] taught them” (Matt. 5:1–2). Then when the “great multitude [that] followed Him” gathered to listen in, Jesus would naturally want to stand to project His voice so that all could hear, as Luke records.
Another possibility is that Luke’s reference to Jesus’ standing is before He gave the sermon while He is still healing people (Luke 6:17–19). Then, since “the whole multitude sought to touch Him” Jesus may have found a place to sit where “He lifted up His eyes toward His disciples and said … [His message]” (6:20). This fits the order given in Luke and would also explain why Matthew declares that Jesus was sitting when He spoke to His disciples. In any event, there is no irreconcilable difference in the two accounts, even assuming they both refer to the same occasion.
“And he came down with them, and stood in the plain, and the company of his disciples, and a great multitude of people out of all Judaea and Jerusalem, and from the sea coast of Tyre and Sidon, which came to hear him, and to be healed of their diseases; (Luke 6:17)”