The snatch is an exercise in expressing power, tension, and just the right amount of relaxation almost simultaneously. 

For starters, the hips power the weight.  While the shoulders and lats certainly help guide the bell, the aggressive hip extension allows the bell to get overhead.  The backswing “loads” the kettlebell like a stone in a slingshot.  The hips are hinged in order to allow the posterior chain to maximally contract and apply force to the bell. 

Now, once we achieve full hip extension, the qualities of tension and dynamic relaxation must balance in order to smoothly direct the trajectory of the bell overhead and land without an impact to the forearms.  On the relaxation front, the arms must stay loose and bend easily to keep the bell from overarching outwards - creating wasted movement and an inefficient trajectory that risk the shoulders and back.  Tension, and just the right kind, comes next to stabilize the lockout.  A step beyond “just stay tight” is the concept of the “active static” contraction wherein the goal is to create a feeling of stability via a paradoxical focus.  In the case of a snatch lockout, the technique includes pushing energy up from the elbow into the bell and pulling down from the elbow into the shoulder socket.