In Frederick Douglass's "What to the slave is the fourth of July?" what does he say the effect of slavery has on white people in the north?

One of Douglass' critical points in the speech is the idea that America has become desensitized to its hypocrisy.  For Douglass, this is what has become of White citizens in the North.  A nation that eloquently articulated the condition of freedom against the British failed to acknowledge the same in the issue of slavery:  "Would you have me argue that man is entitled to liberty?  That he is the rightful owner of his own body?  You have already declared it." Given this reality, American citizens, especially those in the North, have lost a level of sensitivity to the issue.  In the regaling of freedom in the 4th of July, Douglass suggests that American citizens have little ground to celebrate freedom, while the institution of slavery still exists.  What is experienced by Northern and White American citizens cannot be experienced by those who are of color in America:

I say it with a sad sense of disparity between us. I am not included within the pale of this glorious anniversary! Your high independence only reveals the immeasurable distance between us. The blessings in which you this day rejoice are not enjoyed in common. The rich inheritance of justice, liberty, prosperity, and independence bequeathed by your fathers is shared by you, not by me. The sunlight that brought life and healing to you has brought stripes and death to me. This Fourth of July is yours, not mine. You may rejoice, I must mourn. To drag a man in fetters into the grand illuminated temple of liberty, and call upon him to join you in joyous anthems, were inhuman mockery and sacrilegious irony.

In this particular quote, Douglass sees the Fourth of July as an opportunity to awaken the moral conscious of White Americans as they celebrate the spirit of independence, in hopes of expanding this enfranchisement of freedom to all of America's children.