How does "what to the slave is the fourth of july? ” relate to the declaration of independence?

In "What to the Slave is the Fourth of July?" Douglass contradicts the Declaration of Independence. He tells us that the declaration states that the United States is a free country, and this is what people celebrate on the Fourth of July. He also tells us that the declaration states that all men are born equal in the country, and that they have the same rights and privileges. However, he states that all of this is false when you look at the existence of slavery in the country, and how enslaved people have no rights and no privileges.

answer; (external conflict)

imparadis't in one anothers arms  

the happier eden, shall enjoy their fill  

of bliss on bliss, while i to hell am thrust,  

where neither joy nor love, but fierce desire,  

among our other torments not the least,  

still unfulfill'd with pain of longing pines;  

yet let me not forget what i have gain'd  

from their own mouths; all is not theirs it seems:  

one fatal tree there stands of knowledge call'd,  

forbidden them to taste: knowledge forbidd'n?  

suspicious, reasonless. why should their lord  

envie them that? can it be sin to know,