What is the significance of Tom's body being described the way it is?

This description is meant to show how Tom has aged over time. he's different than Nick remembers, hardened and capable of cruelty.

He had changed since his New Haven years. Now he was a sturdy straw-haired man of thirty with a rather hard mouth and a supercilious manner. Two shining arrogant eyes had established dominance over his face and gave him the appearance of always leaning aggressively forward. Not even the effeminate swank of his riding clothes could hide the enormous power of that body — he seemed to fill those glistening boots until he strained the top lacing, and you could see a great pack of muscle shifting when his shoulder moved under his thin coat. It was a body capable of enormous leverage — a cruel body.