What is the main difference between a deficiency in internal control and a material weakness?

 A material weakness presents a higher chance than presented by a "regular" deficiency in internal control that a material misstatement of the company's financial statements will not be prevented or detected on a timely basis.

 A material weakness concerns items on the face of the financial statements while a deficiency in internal control does not. 

A material weakness speaks to bad faith of management, but a "regular" deficiency in internal control emerges despite good faith of management. 

A material weakness causes the auditor to increase their assessment of control risk substantially, while a "regular" deficiency only causes the auditor to increase their assessment of control risk moderately.