“The Second Day of July 1776, will be the most memorable Epocha, in the History of America.–I am apt to believe that it will be celebrated, by succeeding Generations, as the great anniversay Festival. It ought to be commemorated, as the Day of Deliverance by solemn Acts of Devotion to God Almighty. It ought to be solemnized with Pomp and Parade, with Shews, Games, Sports, Gun, Bells, Bonfires and Illuminations from one End of the Continent to the other from this Time forward forever more.
“You will think me transported with Enthusiasm but I am not.–I am well aware of the Toil and Blood and Treasure, that it will cost Us to maintain this Declaration, and support and defend these States.–Yet through all the Gloom I can see the Rays of ravishing Light and Glory. I can see that the End is more than worth all the Means. And that Posterity will tryumph in the Days Transaction, even altho We should rue it, which I trust God We shall not.”
John Adams in a letter to his wife, Abigail, written on July 3, 1776. “The Declaration of Independence” was passed by the Continental Congress on July 2, 1776, which is why Adams expected the celebrations to be on that day. The prinicipal leaders signed the document on July 4, 1776, and that is why our modern celebrations are on that day.
from The Book of Abigail and John: Selected Letters of the Adams Family 1762-1784. ed. by L. H. Butterfield, Marc Friedlaender, and Mary-Jo Kline, Cambridge, MA: Harvard University Press, 1975, page 142