The title was suggested by Steinbeck's first wife after hearing the song, The Battle Hymn of the Republic. "Mine eyes have seen the glory of the coming of the Lord/He is trampling out the vintage where the grapes of wrath are stored." The song by Julia Ward Howe is an allusion to Isaiah 63: 4-6. The novel has allusions to vineyards and grapes throughout to continue the allusion. Steinbeck liked the title because it was a march, and he felt this novel was revolutionary. The title gave it a patriotic flavor as well. Steinbeck was hoping to calm critics who would say it had a Communist leaning.

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What is the significance of the title The Grapes of Wrath and how does it link to human suffering?

The Battle Hymn of the Republic, by Julia Ward Howe, contains this phrase.  She wrote the verses after visiting a Union Army camp during the Civil War. It is an abolitionist anthem, written to further the cause of freedom for all, and the abolition of slavery.

 The first lines are:

Mine eyes have seen the glory of the coming of the Lord / He is trampling out the vintage where the grapes of wrath are stored

Howe uses imagery of God coming to help the cause of those fighting for justice. She set the poem to the tune of John Brown's Body, another abolitionist song concerning the death of John Brown, who led a raid on Harper's Ferry, VA. Brown intended to free and arm slaves. Brown was captured and hanged.