One must remember that Shakespeare wrote in an age where a belief in both the soul and evil were part of their lives and belief system. Church was attended by all and people knew their Bible and could recite from memory numerous passages.
At the beginning of the play, we are led to believe that Macbeth is a good man. He is a great warrior and loyal subject. Three things influence this man to choose the dark side. He admits that he is ambitious, and this coupled with what he is told by the weird sisters and his wife's urgings prove to be too much for him to resist. The temptation is too great.
Macbeth is not a stupid man and knows what will happen if he murders Duncan. In Act I, scene 7, he states"...But in these cases/We still have judgement here, that we but teach/Bloody instructions which, being taught, return/To plague th' inventor."
By Act II, scene 1 he is still having doubt as his mind plays tricks with him. After he kills Duncan, he realizes that he has condemned his soul when he could not say "amen". (Just like Claudius in Hamlet who is unable to pray due to his guilt.) When Lady Macbeth sees that he has brought the daggers with him and tells him to take them back to the murder scene, he cannot do it. This accomplishes two things, Macbeth's fear of his most recent action and Lady Macbeth must physically get the blood on her hands.
From the moment he kills Duncan, he is doomed and he knows it. He kills the grooms to cover his crime. He kills Banquo to cover up his crimes. He murders the Macduff family since he can't murder Macduff himself. (It has been proposed that Macbeth himself was one of the unnamed murders in Act IV, scene 2.)
Another interesting take is the pronunciation of Seyton. In the Ian McKellen, Judi Dench Royal Shakespeare Comapany production, it was pronounced like "Satan".
Is Macbeth evil? Once he turns his back on what he knows to be true and right, he makes some really bad choices. He relies on the supernatural, embracing the dark nature of their power.
Once Macbeth chooses to kill Duncan, he has condemned himself in the world of the play. He made the choices, nobody else. He cannot and does not play the victim card. He fights to the end.
Concerning your question about Shakespeare's Macbeth, I will play the devil's advocate a bit.
I don't know what a human "soul" is, as it is used in this prompt. It seems to me that the term is something that is useful in a work of art like this play, perhaps, but not useful in criticism or discussion of a work of art: it's too imprecise. Strictly speaking, the soul is a second part of a human being that is saved or lost, according to Christian beliefs, which mirror the Greek belief in the dichotomy (different parts) of a human being. If you use the term this way, then your question just refers to evil causing Macbeth to be damned. If this is the case, then the answer is quite simple, perhaps: Macbeth does evil acts, is or becomes evil, then faces eternal damnation, according to Christian beliefs.
But I think the prompt uses soul in a different manner, which is difficult to define. I think it refers to soul in that broad, perhaps undefinable, way used by different people to mean whatever they think it means. The word tends to refer to some deeper part of a human being, some essential part, what makes us tick, so to speak. But the term is so vague that it probably has no place in criticism or literary analysis.
Even if one does use the term in this manner and answers the prompt, however, there is still a problem. Isn't Macbeth evil already? Doesn't the evil come from within Macbeth himself? The prompt seems to identify evil as a separate entity, as if evil somehow influences Macbeth and makes him kill Duncan.
In other words, if Macbeth is evil already, and if the evil comes from within Macbeth, then evil is what Macbeth is and it doesn't destroy anything. Macbeth is evil, and he is ambitious. He kills or orders the killings of numerous people due to his ambition. Evil is not something that destroys Macbeth. Evil is what Macbeth is or becomes.
The prompt, then, has two problems: the way it uses "soul" and the way it uses "evil." I don't know what "soul" is, but Macbeth is evil, most likely even before he hears the witches' predictions, and he is ambitious. And his ambition makes him commit evil acts.
The previous post was quite accurate. I think that the most horrific aspect of the play is how steep the descent into moral oblivion can be and with such little resistance the free fall is. Once Macbeth agonizes over Duncan's killing, it seems like he is on a highway to moral hell. The deaths that follow Duncan lack the agonizing nature and the existential crisis that preceded it. Macbeth's desire to gain more power and to appropriate the world in accordance to his own subjectivity leads to a situation where there is little in way of resistance to evil. The point that might be needed to be made is that once evil is embraced, a sort of moral floodgate opens and the line becomes moved in terms of what is tolerable and intolerable. In Macbeth's case, that line was eradicated fairly quickly.
In Shakespeare's Macbeth, there are plenty of events that suggest that evil can easily destroy the human soul. For example, in Act 5, Lady Macbeth has been driven mad by the acts of evil that Macbeth has committed. She is especially distressed by the murder of Macduff's wife and children. Lady Macbeth knows that they were innocent in the scheme of things, and she is upset by their death. Further, Lady Macbeth understands that she has played a key role in turning Macbeth's views and persuading him to succumb to evil acts. At the beginning of the play, Macbeth wavered at the thought of killing King Duncan, and Lady Macbeth criticized him for being a coward to force him to commit the murder. Now, she knows that her hands are forever dirty (hence her cries that she has a spot of blood on her hands) and she feels guilty about what she has done. Evil has destroyed Lady Macbeth's soul, so she ends her life in suicide.