What does Alain Locke mean by "a spiritual coming of age"?

Alain Locke has been hailed as "the father of the Harlem Renaissance" for his publication in 1925 of The New Negro, an anthology of poems, music, and plays by predominantly African-American artists. During the early 20th century, Harlem became the epicenter of a significant cultural movement, leading to its being called "the capital of black America." At this time, Harlem was a hive of activity, home to a number of African-American artists, musicians, activists, and intellectuals. For Locke, as for many others, the Harlem Renaissance represented a "spiritual coming of age." What he meant by this was that, at long last, the African-American community was able to seize its first real opportunity for group expression and self-determination.
Between 1900 and 1920 the African-American population of New York had grown substantially. Many of those coming to the city were escaping from the systemic persecution and racial injustice of life in the Southern states under Jim Crow. Although the newcomers still faced more than their fair share of prejudice in the North, they were much more free than they could ever have been down South. The Northern economy at that time was stronger, more industrialized, and had far greater job opportunities for African-Americans. This newfound economic independence led to a greater degree of self-confidence and the recovery of a sense of collective racial identity. The spiritual coming of age hailed by Alain Locke, embodied in the rich, vibrant culture of the Harlem Renaissance, was the natural outcome of this significant development.