Weakness of will differs from Laziness

The lazy guy may have decided to do nothing and his laziness may indeed result from an action of a strong will.
As a example, we should decide do to mostly nothing because work is the most polluting human behaviour ever or because inaction may be considered as an efficient path to Taoistic wisdom.

The guy that suffers from a weakness of his will (acrasy) has just no will enough to put himself at work. He may not be lazy at all. But can he will to will more? Is he the master of his will or is the will independent of him? Is not the will free … of us? Alleged “Free will” may be free only in the sense that it does not depend on the self.

Then how can we decide whether a procrastinator is the lazy guy or the one suffering from acrasy?
Christian theology considers laziness as a sin but does it consider the natural weakness of the will?