Read the following excerpt from a speech delivered by a prominent environmental activist:
'We stand at a critical juncture in our planet's history. The choices we make today will reverberate for generations. It is not merely a matter of preserving nature, but of ensuring a sustainable future for our children and grandchildren. We owe it to them to take a stand and champion policies that protect our environment and promote renewable energy sources.
Today, I urge each of you to consider what legacy you wish to leave behind. Will you be the generation that turned a blind eye to the environmental crisis, or will you embrace the call of duty to become stewards of our Earth?'
Based on the excerpt, what is the primary purpose of the activist's speech, and who is the intended audience?