Macbeth takes a journey as a character and in Act I, scene 7, we hear his inner thoughts as he weighs everything. He definitely has opportunity since the king is visiting.
In this speech, he gives all the reasons he can think of not to kill Duncan. He is his subject and also a kinsmen, plus he is his host. If Duncan had been an evil or a bad king, his murder could be justified but Duncan has been a good king. He knows that if he kills Duncan, he will die a violent death. He reasons that his ambition just isn't enough for him to kill Duncan and has decided against killing him. At this point we can feel for Macbeth.
By the time we get to Act IV, scene 1 he has gone down the the highway to hell, so to speak. He has killed Duncan and the grooms and framed Malcolm and Donalbain. He has killed Banquo and tried to kill Fleance. In this scene he has sought out the witches for information. He doesn't like what he sees at the end of this encounter since it concerns Banquo and his line of future kings. He damns all who trust them and in so doing, damns himself. At this point, it is difficult to have any sympathy for Macbeth. He is too steeped in innocent blood.
I have given you information about Macbeth and what those lines are about, it is your job to find the textual support since it is your paper.