The line is from Chilean poet Pablo Neruda's autobiography, Memoirs. The line references his political awakening at the time of the Spanish Civil War. Neruda had befriended the Spanish poet Federico Garcia Lorca prior to Lorca's murder by Fascists in the 1930s. As a result, Neruda became staunchly antifascist and supported the loyalist cause in the war. And he continued to support the antifascist cause upon his return to his native Chile.
On a larger level, Neruda is saying that his poetry will no longer be exclusively introspective and personal. Poetry, he had learned, could be democratic and political and speak to collective society. Later in his life, Neruda would take the political cause further and become a diplomat.
The twentieth century was the most violent century in human history, wracked by two world wars and innumerable revolutions. This had an enormous intellectual and artistic impact on several generations. Most of the great art of the twentieth century, whether in the form of prose, poetry, or painting, spoke to the cataclysmic changes that were taking effect across the globe.
By speaking to the people through his poetry, Neruda is hoping to heal their wounds and offer his art as a political weapon in the fight for truth and justice.