Consider first that the Harlem Renaiassance was the first and biggest contribution to literature, music, and art, by the black culture in America.  It happened post-slavery but pre-civil rights.  In an effort to really make their unique voices heard, these men and women drew from their own cultural heritage to create something that was very personal and very different from what the rest of America was reading, writing, singing and dancing to.

Language techniques used: dialect (which drew largely from the rhythm of negro spirituals and later jazz music and the blues), experience specific diction (much of this drawing from the journey out of slavery) and creative poetic license when it came to grammar, spelling, and complete sentences.  (Example: Langston Hughes)

One significance of these changes is the fact that they are still used in and have greatly influenced art and literature today.  Consider Maya Angelou, Alice Walker, James McBride.  Consider the progression of hip-hop from the 80s until now.  Consider the impact of jazz on the music world.

Another significance is the way the Harlem Renaissance has managed to alter attitudes.  The very word "renaissance" means re-birth.  This was a re-birth for black Americans at a time in our history when racial tension was still very high and segregation a way of life.  By creating a voice through something so positive as art and literature, the Harlem Renaissance managed to begin building a bridge between two cultures in possibly the most peaceful way it has ever been done.