Why is two-way communication (feedback) an important aspect of effective communication?

Two-way communication is an important aspect of effective communication because it stirs a conversation.
The conversation then provides feedback for the conversation starter that can help him/her with the product or message they are trying to get across.  It is important that the audience receives the message, pays attention to the message, understands the message and knows it is credible and memorable, and acts on the message.