Matthew 5:1-2,  Jesus ascends the mount and prepares to speak

5:1Seeing the multitudes, he went up onto the mountain. When he had sat down, his disciples came to him.
5:2 He opened his mouth and taught them, saying,

(Matt 5:1-2 WEB)

Ascending the mountain

The first two verses of Matthew 5, meticulously set the stage for what was about to happen. Jesus retired from the crowds and sought out a nearby hill, just as Moses had when the Ten Commandments were given on the first ever Day of Pentecost. Then Matthew deliberately calls this Galilean hill a “mountain”, in order to emphasise the teaching’s relationship to the law-giving on Mount Sinai.

There is some dispute over which hill Jesus went up, but there are two primary candidates:

The Mount of the Beatitudes, a hill near the NW coast of the Sea of Galilee, is now marked by the octagonal Church of the Beatitudes.

The Horns of Hattin lie about 20Km to the SW of Capernaum.

Jesus’ disciples had followed him up the mountain to learn from him, so he sat down, thus signalling, in the accepted manner of a Jewish teacher (a Rabbi), that they should pay attention.

Once Jesus was seated, Matthew says that he opened his mouth. Which was, within Judaism, the accepted way of indicating that something worth hearing was about to be reported.

Matt 5:1-2 in detail.