How does the porters scebe increase tension and suspende?

In the scene just prior to the porter's, the audience witnesses the reaction of the Macbeths to Duncan's murder, and it is a very tense scene. Macbeth is in a panic, thinking he'll never have clean hands again, and Lady Macbeth is chastising him for bringing the daggers from the room and calling him a coward for being unable to go back or pull himself together. They hear the knocking at the door even ...

In the scene just prior to the porter's, the audience witnesses the reaction of the Macbeth to Duncan's murder, and it is a very tense scene