How is Macbeth a man of great potential and noble stature?and why ?

The character of Macbeth in Shakespeare's Macbeth is a man of great potential and noble stature.  He pretty much has to be to fulfill the role of tragic figure in Elizabethan theatre. 

The idea is that in order to do the level of great harm expected in a revenge tragedy, a character must be in a position of great power.  A commoner, for instance, does not have the kind of power, influence, and authority to do great harm to an entire kingdom.  A tragic figure must have this kind of power, influence, and authority.

Macbeth does.  He appears at the beginning of the play to be second-in-command of the military, second only to King Duncan.  And, in fact, Duncan does not appear in any way to direct the battle and be involved in any specific way.  He relies on others.  Also, Macbeth's position of authority is confirmed when Duncan is murdered and his heirs flee, and Macbeth is made king. 

Second, Macbeth is a castle owner, which means he is wealthy and influential.  He is a noble, though between his winning the battle at the beginning of the play, and his own fearless death, he doesn't act very nobly.