In this video, Jeremy uses some footage of Sam Snead, Jordan Spieth, and Rory Mcilroy to explain left bend and extension in the backswing as well as the lowering, rotation, and extension pieces of the downswing.
Jeremy explains in full detail Snead did such a tremendous job of extending and going into left bend in his backswing. This allowed him to get to his left side easily while lowering and rotating in transition -- setting him up to work up out of the ground and extend towards the target through impact.