Final answer:
In Shakespeare's play 'Macbeth', the central character Macbeth is the speaker of many traditionally significant speeches within the play. Lady Macbeth also delivers powerful lines, but Macbeth's speeches are integral to exploring the main themes.
Step-by-step explanation:
The speaker in the traditionally significant speech of a Shakespearean play, specifically in Macbeth, is often a central character who drives the plot forward. In Macbeth, the titular character, Macbeth, himself is frequently the speaker of important soliloquies and dialogues that reveal his thoughts and ambitions. Lady Macbeth, another central figure, is also known for her influential speeches, especially those that manipulate Macbeth into committing regicide.
For example, we see Macbeth, as a character who deeply contemplates his fate and the consequences of his actions, deliver many significant speeches. The passage shown in the question, where Macbeth interacts with the witches and later contemplates their prophecies, illustrates Macbeth's pivotal role as a speaker. Moreover, the lines spoken by Lady Macbeth as she descends into madness and guilt also reflect her role as a keystone speaker within the text.
In the context of the question provided, Macbeth is the character who delivers some of the play's most traditionally significant speeches. While Lady Macbeth and other characters like Banquo and Duncan contribute to the play's rich dialogue, it is Macbeth's lines that most often carry the weight of Shakespeare's thematic explorations. Thus, Macbeth would be the most fitting answer if one must choose a speaker with traditionally significant speeches in the play Macbeth.