Why do Casy and Tom help with the strike? What was the strike about? What were the outcomes of the strike?

Casy believes himself to support a just cause. He claims that people who strive for justice always face opposition, citing Lincoln and Washington, as well as the martyrs of the French Revolution. Tom, who has been able to separate himself thus far, is drawn into the group of strikers when a man hits Casy in the head with a pick handle. 

The strike is the catalyst of another tragedy for the Joad family. Soon after Tom finds the striking workers, he is reunited with Jim Casy, who has been released from jail and has found a new purpose as a labor activist. His lost religious zeal has been transformed into working-class activism, charged by his experiences in jail and his travels within California. Casy is a crusader for the cause of the workers; the indecision over his role as a preacher earlier in the novel has been replaced by a fiery conviction concerning the justice of laborers' rights. There are strong political overtones to the final scenes with Casy, who compares the cause of labor to the missions of Lincoln, Washington, and the patriots of the French Revolution. Steinbeck makes it clear that the labor activists are facing certain doom, but that they will be vindicated eventually. Casy, who sacrificed his freedom for Tom earlier in the novel, makes a final sacrifice in this chapter, the victim of a brutal murder at the hands of the police. Casy has now been a martyr for both the Joad family and the entire class that the Joads represent.

The effect of this martyrdom is that Tom must now leave Hooper ranch to escape capture by the police. Although he wishes to go alone, Ma Joad once again binds the Joad family together. She chooses to risk the safety of the entire family to preserve whatever unity the family has left.