{He went up into the mountain} (aneb(8820)eis to oros). Not "a"
mountain as the Authorized Version has it. The Greek article is
poorly handled in most English versions. We do not know what
mountain it was. It was the one there where Jesus and the crowds
were. "Delitzsch calls the Mount of Beatitudes the Sinai of the
New Testament" (Vincent). He apparently went up to get in closer
contact with the disciples, "seeing the multitudes." Luke ( Lu
6:12 ) says that he went out into the mountain to pray, Mark ( Mr
3:13 ) that he went up and called the twelve. All three purposes
are true. Luke adds that after a whole night in prayer and after
the choice of the twelve Jesus came down to a level place on the
mountain and spoke to the multitudes from Judea to Phoenicia. The
crowds are great in both Matthew and in Luke and include
disciples and the other crowds. There is no real difficulty in
considering the Sermon on the Mount in Matthew and the Sermon on
the Plain in Luke as one and the same. See full discussion in my
_Harmony of the Gospels_.