The only constant is change. It's an age-old truism that's been born out repeatedly over the past year.
In January, when Democrats arrived in Philadelphia to lick their wounds after a sound defeat in November's midterm elections, I sat in the press area in the Society Hill Sheraton, listening as President Obama told Democrats, "Even though [Republican] policies haven't quite caught up yet, their rhetoric is starting to sound pretty Democratic."
At the time, former Republican presidential candidate Mitt Romney was focused on poverty as a Republican priority. Since then, the pendulum has swung completely in the opposite direction, as Donald Trump has moved atop Republican presidential polls with rhetoric that insults and demeans women, people of color, Muslims, and ethnic minorities.
Things changed even more quickly on the international stage.
In February, when the chaos of the Syrian civil war set the stage for the rise of ISIS, President Obama asked Congress for a three-year authorization for use of military force against the group. At the time, Obama said, "ISIL is on the defensive, and ISIL is going to lose."
Things changed. Since then, the group the president refers to as ISIL has killed thousands in the Middle East and 130 in a coordinated attack in Paris and allegedly inspired a couple to kill 14 people in San Bernardino, Calif.
But there were other changes that turned 2015 from a year of anxiety to one of questions.
The historic six-month state budget impasse has left schools and non-profits without the funding they need to serve our most vulnerable populations. Never in modern history has Pennsylvania seen a budget battle go this long. Which raises a question: Why are the state legislators who have thus far failed to pass a budget being paid when schools are not?
Here's another question: Why did the Philadelphia School District outsource management of its substitute-teaching services to Source 4 Teachers in a contract worth up to $35 million in April? Especially since 64 percent of vacancies were filled by substitutes prior to the deal, but the number dropped to around 30 percent by November.
Even as we struggled to find answers to those questions, 2015 brought us tragedy.
In June, Dylann Roof, 21, sat through an hour of bible study in Charleston, S.C., and then killed nine black worshippers, including S.C. State Sen. Clementa Pinckney, who was a pastor at the Emanuel A.M.E. church where the shootings took place.
In the wake of that horror, heroes emerged, and their actions brought about change.
There was Bree Newsome, the African American woman who was arrested after climbing the flagpole outside the South Carolina Statehouse and removing the Confederate flag that had flown there for more than 50 years.
There were the families of the victims, many who forgave the shooter rather than engage in the hate that drove him.
There was South Carolina State Rep. Jenny Horne, a white woman who stood on the House floor and in a fiery speech demanded the permanent removal of the flag.
There were ordinary Americans across the country who engaged in the discussion of hate, history, and heritage that eventually caused the flag to come down, not only in South Carolina, but in places all over America.
That engagement made 2015 more than a year of change. It made 2015 a year of action. In the face of tragedy and hate, terror and trauma, we demanded more. We granted forgiveness. We looked to the future.
I can't wait to see what 2016 will bring, but I know one thing is guaranteed - change.