In one of my parishes, I was shown by a parishioner a video Life of Christ, following closely the text of S Matthew's Gospel.
I enjoyed it and was grateful to him. But one detail jarred.
At the beginning of Chapter 5, the Sermon on the Mount, the Evangelist takes the trouble explicitly to make clear that the Lord taught sitting down (kathisantos autou). Yet the film-maker showed Him walking round and through the crowd, up and down, and expounding his teaching with immense and engaging vividness and interpersonal interaction.
Rather like ... er ... a very winsome and charismatic schoolmaster.
I prefer the explanation of Professor Ratzinger:
"Jesus [is] the new Moses ... The opening verse is far more than a casual introduction: 'Seeing the crowds, he went up on the mountain, and when he sat down his disciples came to him.' ... Jesus sits down--the expression of the plenary authority of the teacher. He takes his seat on the cathedra of the mountain. ... Jesus takes his seat on the cathedra as the teacher of Israel and as the teacher of people everywhere. Hearing ... is the basis on which a more inclusive Israel is built--a renewed Israel, which does not exclude or revoke the old one, but steps beyond it into the domain of universality ... Jesus sits on the cathedra of Moses ... he sits there as the greater Moses, who broadens the Covenant to include all nations. ... the very fact that it is the scene of Jesus'preaching makes it simply 'the mountain'--the new Sinai. The 'mountain' is the place where Jesus prays--where he is face to face with the Father. And that is exactly why it is also the place of his teaching, since the teaching comes forth from this most intimate exchange with the Father. The 'mountain', then, is by the very nature of the case established as the new and definitive Sinai. ..."
In Archdeacon Allen's old ICC commentary on Matthew, the writer merely comments that kathisantos ktl is an unclassical misuse of the genitive 'absolute' construction, and offers a reference to Blass! I am reminded of the gentle irony of Dix's reference to "the Greek Play Bishops of [the 1870s]".