One of the more powerful attributes of Martin Luther King's I Have a Dream speech is his use of allusions to historical documents. He is attempting to explain how many of the freedoms promised to American citizens have been denied to African-Americans. First, he references the Emancipation Proclamation, but quickly turns to the Constitution and Declaration of Independence. He directly alludes to the Declaration of Independence in this passage:
When the architects of our republic wrote the magnificent words of the Constitution and the Declaration of Independence, they were signing a promissory note to which every American was to fall heir.
He goes on to actually to reference some important lines in the Declaration of Independence, including what Thomas Jefferson called the unalienable rights of "life, liberty, and the pursuit of happiness." King is comparing these rights to a check that cannot be cashed because the bank of justice is bankrupt. That is also a skillful use of allusion on his part.
King was a baptist preacher, so it would stand to reason that he would have biblical references in his speech. Included below are parts from his speech compared to passages in the Bible.
"It came as a joyous daybreak to end the long night of their captivity." (King Speech) "For his anger endureth but a moment; in his favour is life: weeping may endure for a night, but joy cometh in the morning." (Psalm 30:5)
"...finds himself an exile in his own land." (King speech)
"So Israel was carried away into exile from their own land to Assyria until this day." (2 Kings 17:23)
"Let us not seek to satisfy our thirst for freedom by drinking from the cup of bitterness and hatred." (King speech) "You cannot drink the cup of the Lord and the cup of demons too; you cannot have a part in both the Lord's table and the table of demons." (1 Corinthians 10:21)
These are just three biblical references in the speech, but there are over fifteen such allusions to scripture in the address.