The phrase 'into his manhood' is Mama's own description of Walter Lee Younger at the climax of Lorraine Hansberry's A Raisin in the Sun. To trace this transformation is to follow Walter from a frustrated, self-pitying dreamer to a man who reclaims his dignity by choosing family and self-respect over money.
Walter at the start: immaturity and obsession with money. At the opening Walter is a chauffeur consumed by resentment. He measures manhood by wealth, dreams obsessively of a liquor-store investment, and quarrels with his wife Ruth and sister Beneatha. He is impatient, self-centred and blind to the feelings of others, seeing his father's insurance money only as a means to his personal ambition.
The fall: loss of the money. Trusted by Mama with the remaining funds, Walter hands the money, including Beneatha's school fees, to Willy Harris, who absconds with it. This betrayal is Walter's lowest point. Humiliated and desperate, he resolves to accept Karl Lindner's offer to buy the family out of Clybourne Park, willing to swallow his pride for cash.
The turning point: Lindner's return. As Lindner arrives to complete the deal, Walter is forced to confront what accepting the money would mean. Standing before his young son Travis, he cannot bring himself to sell the family's dignity. He tells Lindner that the Youngers will move into the house because his father earned it brick by brick.
Arrival at manhood. In that refusal Walter finally becomes the head of the family in the true sense, valuing pride, heritage and the welfare of his people above money. Mama recognises the change, saying he has finally come into his manhood, comparing him to a rainbow after rain.
In conclusion, Walter's transformation is a moral growth from a materialistic, self-absorbed dreamer to a responsible man who defines manhood by dignity and family loyalty. His journey embodies the play's affirmation of black pride and human worth.