But when it became day he called his disciples to him and chose from among them twelve, whom he also named apostles.”​—Luke 6:12, 13.

Following this, Jesus “came down with them and took his station on a level place, and there was a great crowd of his disciples, and a great multitude of people from all of Judea and Jerusalem and the maritime country of Tyre and Sidon, who came to hear him and be healed of their sicknesses.

Luke 6:17-20.

Hence, the Sermon on the Mount was given shortly after Jesus had chosen his 12 apostles. This was evidently in 31 C.E., at about the halfway point of his three-and-a-half-year-long earthly ministry. Although “a great multitude of people” from all over Palestine heard the sermon, the Scriptural record indicates that Jesus spoke mainly for the benefit of his disciples.​—Matt. 5:1, 2; Luke 6:17, 20.