How is macbeth’s conflict intensified by the events in scene 4? what lines from his aside in scene 4(lines 48-53) develops the audiences understanding of this conflict?

1. During the events of Scene IV, Duncan announces that his successor will be his own son, Malcolm. This obviously angers Macbeth because he thought the next king would be him, as prophesied by the three witches. This is the moment when he decides for certain that he has to kill Duncan if he wants to take the throne for himself. He concocted a plan along with his wife, and together they murdered the king. 

2. This is his aside which he says in the scene:

(aside) The prince of Cumberland! That is a step
On which I must fall down, or else o'erleap,
For in my way it lies. Stars, hide your fires;
Let not light see my black and deep desires.
The eye wink at the hand, yet let that be
Which the eye fears, when it is done, to see.

As you can see here, what Macbeth is showing is his contempt for Malcolm who will become king just because his father is the king at the moment, so he can inherit the throne regardless of whether he deserves it or not. Macbeth believes he should be the one to get the throne because of his accomplishments, and because of the prophecy which said he would get it eventually. In this aside, he is showing us that he has dark thoughts, meaning that this is the moment when he realized that he has to kill Duncan in order to fulfill his goals.