The painting will forever bear witness. Picasso's first political statement of his life reads as follows:

The war in Spain is a war of reaction against the people, against liberty. My whole life as an artist has been a continual struggle against the reaction, and the death of art. In the picture I'm now painting, which I shall call Guernica, and in all my recent work, I am expressing my horror of the military caste which is now plunging Spain into an ocean of misery and death (Daix 251).

Picasso felt that he couldn't escape his duty as he saw it; but he knew that by perserving he risked losing everything. The bombs touched the depths of his personal unhappiness. The result was the passion he poured into Guernica (251).

Sources:

Daix, Pierre. Picasso Life and Art. New York. HarperCollins, 1987.