When John was thrown in prison, Jesus backed away from Jerusalem, choosing to live in Galilee. At the same time, though, He took up John’s declaration: “Repent, for the kingdom of heaven has come near” (Matthew 3:2, 4:17). As he taught, proclaimed, and healed the sick (Matthew 4:23), people started to follow Him. Before long, the crowd grew so large that Jesus had to climb a little way up the side of a mountain so everyone could hear him.
He sat down, drew His disciples to the front row, and began to teach the people. I imagine He scanned the crowd, praying silently, and took a deep breath before He began. (With no amplification, He would have needed to project His voice, and that takes some lung power.)