Sc. 1, Lines 144-154: What does Macbeth's speech reveal about his changing character? How does his speech develop a theme of the drama?

The speech in the lines 144-154 i Act IV scene i presents a different quality in the character of Macbeth. He is shown as a completely different person, ready to do anything to get his power, even to the extent of killing innocent people.

This speech provides a motive for Macduff to attack Macbeth and avenge the death of his household.

Explanation:

In Act IV scene i of William Shakespeare's "Macbeth", Macbeth is seen in conversation with the witches and then later on, he was told by Lennox that Macduff has fled to England. This made him angry and was the very scene where he decided to go through with whatever he decided, instead of waiting for an opportune time.

In the lines between 114 to 154, Macbeth declares that he will raid Macduff's place and kill everyone. This is in stark contrast to his previous personality, where he had to be coaxed and pressured on by his wife to do anything. He also is deviating from his usual murdering of those who are an obstacle to his attaining the throne. Rather, he is now fine with killing innocent people too.

This speech of Macbeth moves the plot forward with his act of actually killing everyone in Macduff's household. It provides a motive for Macduff to confront and avenge his family from "this fiend of Scotland".