And seeing the multitudes ,.... The great concourse of people that followed him from the places before mentioned,
he went up into a mountain ; either to pray alone, which was sometimes his custom to do, or to shun the multitude; or rather, because it was a commodious place for teaching the people:
and when he was set : not for rest, but in order to teach; for sitting was the posture of masters, or teachers, see Matthew 13:2 Luke 4:20 . The form in which the master and his disciples sat is thus described by Maimonides
"The master sits at the head, or in the chief place, and the disciples before him in a circuit, like a crown; so that they all see the master, and hear his words; and the master may not sit upon a seat, and the scholars upon the ground; but either all upon the earth, or upon seats: indeed from the beginning, or formerly, היה הרב יושב "the master used to sit", and the disciples stand; but before the destruction of the second temple, all used to teach their disciples as they were sitting.'
With respect to this latter custom, the Talmudists say
"from the days of Moses, to Rabban Gamaliel (the master of the Apostle Paul), they did not learn the law, unless standing; after Rabban Gamaliel died, sickness came into the world, and they learnt the law sitting: hence it is a tradition, that after Rabban Gamaliel died, the glory of the law ceased.'
His disciples came unto him ; not only the twelve, but the company, or multitude, of his disciples, Luke 6:17 which he made in the several places, where he had been preaching; for the number of his disciples was larger than John's.