There are three essential movements of the body in the swing and you need to know them all and how they impact what you do. You’ve got lateral motion — towards and away from the target; vertical motion — up and down; and rotary motion. As you swing, you’ve got a lateral motion as the club goes straight back, which turns into a rotary motion, which then turns into a vertical motion.
At the top, you begin the downswing by moving lateral and vertical down into your lead foot. From there, you’re going to push up and around your lead foot. Knowing what you’re doing and the sequence in which you’re doing it is massively important to making consistent contact.