The theme of Macbeth is "Vaulting ambition, which o'erlaps itself / And falls on the other." With every murder Macbeth thinks that he gains his object, and it is the last. But he still has his ambition which pushes him further. Having obtained the crown, he is further ambitious to keep it in his own family. Surely, just one more murder gives him all he wants, and so it goes on.
After the first confrontation with the witches, Macbeth becomes worried that he may have to commit a murder to gain the throne, but he fears the consequences. In his first lengthy soliloquy, Macbeth is strongly conscious of the gravity of the act of regicide. He acknowledges that "bloody instructions" come back to trouble the person who thinks of them. The idea of a moral order is present in this scene, but in muted form. Macbeth knows what he does is wrong, and he recognizes that there will surely be consequences. In addition, he reveals that he may be initiating a cycle of violence that will eventually destroy him.
After Macbeth commits the first murder of killing Duncan, he seems to have gotten used to the idea as by this point the body count has risen to alarming levels. As soon as the first murder happens, Macbeth kills the King's guards to clear himself. From now he is moving towards his downfall as he kills innocent people.Then, his first crime leads him to commit another crime which is the murder of Banquo because he knows of the prophecy and to prevent its second part from becoming true.
By the murder of Bnaquo, the play's main theme, the repercussions of acting on ambition without moral constraint, becomes clear and true. The play builds inflexibly towards its end while Macbeth's actions seems to develop inevitably. The audience knows that there is nothing to stop Macbeth's murder spree his own death. Later on, the murder of Lady Macduff and her son marks the moment in which Macbeth descends into utter madness, killing neither for political gain nor to silence an enemy, but simply out for a furious desire to do harm. After saying, previously, 'There is none but he (Banquo) whose being I do fear,' he shows fear of Macduff's family seems to accord his vow; 'The very firstlings of my heart shall be the firstlings of my hand.' This shows clearly the theme of cyclical nature of evil.
In conclusion, Macbeth has no sooner sinned than he loses joy of the fruits of his sin. The happiness he has looked for gets further and further away as each new crime increases his remorse and fear. Shakespearian tragedy goes down to the root of things. The struggle in Macbeth is a symbol of the struggle between good and evil in men; goodness and evil each brings its own reward.