In the Gospel according to St. Matthew, the Sermon on the Mount is contained in chapters 5-7.  It is parralled in Luke's Sermon on the Plain, in Luje 6:20-49.  Judging by the scenery, this window could depict either, although the former is the title.

 

Jesus is depicted teaching a diverse crowd, some listening attentiveely, others are distracted or disinterested.

 

Top window:  Book of Life, the Alpha and the Omega from the Greek alphabet, the first and the last letters.

 

Scripture:  Rev. 1:8, 21:6 (God) Rev. 22:13 (Jesus).  Also, Isa. 44:6, John 1:1-3.