what is the dramatic importance of Dagger scene in Shakespeare's drama 'Macbeth'

The dagger scene represents Macbeth's very conflicted feelings about killing the King. He wants to live up to the manly deed that L. Macbeth expects him to perform. At the same time, he doesn't really want to kill Duncan for a variety of reasons (he should be protecting him, he is related to Duncan, he fears God's judgment). Macbeth interprets the illusion of the dagger as a product of his stressed out, "heat oppressed", brain. The dagger taunts and challenges Macbeth to ascend the stairs very much like his own wife taunts and challenges his manhood.