What is suggested about Macbeth's character through his hiring murderers to carry out his plan?
The fact that Macbeth employs others to do his dirty work for him most clearly depicts just how far from grace he has fallen. He has lost all integrity and is overwhelmed by a desire to maintain power. The once noble and courageous general has now become a paranoid, evil tyrant who will stop at nothing to retain control. Macbeth has become so ruthless and bloodthirsty that he himself acknowledges that he is so deeply steeped in blood that there is no turning back.
Macbeth's evil is beyond redemption because he instructs his assassins not only to kill those whom he mistrusts but also to annihilate his enemies' families. He, for example, instructs his hired killers to not kill only his best friend and confidante, Banquo, but to also murder Banquo's son, Fleance. The depth of his moral turpitude is emphasized by the fact that he blatantly lies to the murderers by informing them that Banquo was responsible for their incarceration and misery. The killers are riled by this accusation and are more than willing to destroy the one they deem an enemy.
Macbeth later hires assassins to kill not only Macduff's entire family but everyone in Macduff's employ. He has become so vengeful and spiteful that he deliberately sets out to hurt those whom he believes have turned against him by targeting everyone associated with them. These actions also illustrate just how dependent Macbeth has become on the advice of the witches. He is led by superstition and has become gullible enough to believe their every word. He apparently does not trust his own judgment and takes whatever they say or advise as indefatigable truths.
Practically all of Macbeth's actions are informed by what he learns from the witches. They told him that Banquo's royal lineage would continue while his own would end. The weird sisters also told him to "beware Macduff." In both instances, the evil dictator enacted his heinous atrocities in an attempt to safeguard his destiny.
Macbeth has devolved from a trusted, patriotic, respected, and heroic leader into a cowardly, piteous, and merciless tyrant. In the process, he has not only destroyed himself but also everything he once held dear: his king, his beloved wife, and his most trusted confidantes and friends. Furthermore, his malicious zeal and ignominy have almost destroyed his country.
Macbeth makes his purpose in hiring the murderers clear to them; as king, he could simply order Banquo and Fleance to be killed, but they share certain friends and influential contacts, whom Macbeth needs on his side. Being the sort of king that orders seemingly frivolous executions, especially of those who were once close to him, is sure to turn suspicions and paranoia against him and make it harder for him to rule. Macbeth also cannot reveal that he needs Banquo and Fleance murdered because of a pagan prophecy, because this would surely mark him as an enemy of all. Instead, Macbeth lies that he hates Banquo, for specific reasons unstated, but this is enough to convince the murderers that he is on their side.
All of this suggests that Duncan's death did not mark an end to the conspiracies that Macbeth is obliged to contrive in order to keep his power. Macbeth is also more concerned than ever by the witches' prophecy, and is either unaware of, or ok with the fact that his actions may actually be fostering the prophecy rather than counteracting it. It also shows that Macbeth is now "above" murder; having done the deed himself, he might be seeing it as a lowly act, to be performed by servants, and this suggests that his lessening regard for human life renders it as a commodity rather than precious.