A speech should never be a monologue. Leave those to actors and poets. Although you do most of the talking (unless you have a serious heckler), you still get feedback in the form of expressions, body language, laughter and applause. You need to be responsive to the signs. In order to do that, you need to watch your audience, not bury your head in your script.
Your audience does not want you to talk at them. They don't want you to talk to them. They want you to talk with them. This reinforces the sense that you and your audience are "in this together", on the same side. A speaker that ignores the response of an audience can appear confrontational, while one who appears not to notice an audience at all can appear distant. Neither of these approaches will help you to deliver your message.
The way that you make eye contact, the way you gesture towards your audience and the way you move around the stage can all have a significant effect on how you are perceived. Stand-up comedians will alter their act, bringing forward their best material from the end of their performance if they aren't getting laughs. You also need to be prepared to adapt if the audience are not in tune with what you are saying. For example, if many members of the audience look puzzled, you may need to go back a few steps and explain yourself in more detail. On the other hand, if they look bored, you may need to pick up the pace.
It's a conversation.