What does Matthew 5:1 mean?

Matthew 5:1 KJV
And seeing the multitudes, he went up into a mountain: and when he was set, his disciples came unto him:

Matthew 5:1 NKJV
And seeing the multitudes, He went up on a mountain, and when He was seated His disciples came to Him.

Matthew 5:1 MKJV
And seeing the multitudes, He went up into a mountain. And when He had sat down, His disciples came to Him.

Matthew 5:1 KJV 2000
And seeing the multitudes, he went up into a mountain: and when he had sat down, his disciples came unto him:

Interlinear KJV

And /de/ seeing /eido/ the multitudes, /ochlos/ he went up /anabaino/ into /eis/ a mountain: /oros/ and /kai/ when he /autos/ was set, /kathizo/ his /autos/ disciples /mathetes/ came /proserchomai/ unto him: /autos/

Albert Barnes’ Commentary

Verse 1. Seeing the multitudes The great numbers that came to attend on his ministry. The substance of this discourse is recorded in the sixth chapter of Luke. It is commonly called the sermon on the mount. It is not improbable that it was repeated, in substance, on different occasions, and to different people. At those times, parts of it might have been omitted, and Luke may have recorded it as it was pronounced on one of these occasions. See Barnes “Lu 6:17-20”.

Went up into a mountain. This mountain, or hill, was somewhere in the vicinity of Capernaum, but where precisely is not mentioned. He ascended the hill, doubtless, because it was more convenient to address the multitude from an eminence, than on the same level with them. A hill or mountain is still shown a short distance to the northwest of the ancient site of Capernaum, which tradition reports to have been the place where this sermon was delivered, and which is called on the maps the Mount of Beatitudes. But there is no positive evidence that this is the place where this discourse was uttered.

And when he was set. This was the common mode of teaching among the Jews, Lu 4:20; 5:3; Joh 8:2; Ac 13:14; 16:13.His disciples came. The word disciples means learners; those who are taught. Here it is put for those who attended on the ministry of Jesus, and does not imply that they were all Christians. See Joh 6:66.