What is the significance of Juneteenth?

In 1863, President Lincoln had just signed the Emancipation Proclamation in January. With a Union victory, the slaves would be freed, and as the Civil War progressed, a Union victory became more inevitable. As you might imagine, the word of Lincoln's Emancipation Proclamation would take many months before it spread to all parts of the continental United States. Communication in the 1860s was somewhat limited, and slave owners would have absolutely no reason to assist Lincoln or his supporters in spreading the word.
As the war began to wind down in 1865, western states would be the last to receive notification of the war's end and conclusion. With the end of the Civil War in 1865, two years after President Lincoln signed the Emancipation Proclamation, many enslaved African Americans were unaware the war had concluded with a Union victory and that they were now legally free. On June 19 of 1865, Gordon Granger, a Union General, arrived in Galveston, Texas to announce the end of the war and to read the Emancipation Proclamation, freeing an estimated 250,000 slaves in Texas. The announcement over time became commemorated as Juneteenth.
Juneteenth is sometimes referred to as the second Independence Day by several prominent African American leaders. It is significant in history, as it celebrates the end of the institution of slavery in the United States. Texas was the first state to commemorate Juneteenth as an official holiday in 1980, and since that time all but 4 states have set June 19 aside as a state or ceremonial holiday.
The popularity of the date continues to grow as a greater number of historians, political leaders, and citizens recognize significant contributions to American society by African Americans and the need to recognize those contributions as integral to an integrated American identity.
Juneteenth celebrations are family affairs and have become increasingly popular with many segments of American society who want to keep civil rights issues at the forefront of the American mind and desire to educate citizens as to the struggles of African Americans in United States history.
https://www.history.com/news/what-is-juneteenth

https://www.juneteenth.com/history.htm

https://www.nationalgeographic.com/culture/holidays/reference/juneteenth/