conceal these murders from others ("blindfold the kindhearted day").

As Macbeth continues, he urges the night to use its "bloody and invisible" hand to commit these murders and so bring about an end to Macbeth's "fear." Remember that Macbeth is afraid of the prophecy in which it was foretold that Banquo's sons would be the kings of Scotland. As such, Macbeth wants to protect his crown and is prepared to go to any lengths to ensure that Banquo's sons do not take it from him.

In the next lines, Macbeth likens himself to a predator who awakens in the night to hunt his prey, represented here by Banquo and Fleance. This is significant because he is suggesting that these murders are legitimate--that they are an inevitable part of the natural order and that they cannot be avoided.

Macbeth has become intimate with the powers of darkness through the course of the play.  He first invoked the power of darkness in Act 1, sc. 4, right after Duncan has named his son Malcolm as the Prince of Cumberland to succeed him to the throne.  Macbeth says, in an aside, "Stars, hide your fires / Let not light see my black and deep desires."  Darkness literally and figuratively hides many deeds that Macbeth and Lady Macbeth do not want seen.  Darkness also represents evil which grows in intensity in the play.  Macbeth has Banquo killed because he fears that Banquo may suspect he had something to do with Duncan's murder but he also has Banquo killed because he is jealous of Banquo.  The witches told Banquo that his sons would be kings and Macbeth hopes to stop that by killing both Banquo and his son, Fleance.  These are evil acts and Macbeth does not want the light of truth or the light of day to reveal them for what they are - simple murder.