Tom is saying goodbye to his mother and turning himself into a presence rather than a person who can be caught. The speech echoes the preacher Casy, and it echoes the labor wars Steinbeck had been reporting. It is a character’s promise, in a dialect he took from the road, and it has been recited at enough rallies to become a hymn. The novel does not pretend the promise is easy to keep. It says the alternative is Ma’s fear that a man can break.