Abolition had to begin somewhere in the United States. Pennsylvania seems a likely location due to it's proximity to Washington D.C. and having been a temporary capital of the country. Though it took a multitude of tried and failed initiatives, each was a small step leading in the direction that eventually abolished slavery in the United States.
The gradual abolition of slavery act helped to ensure that no new slaves would be born in Pennsylvania. It was the first step towards eliminating slavery altogether in that state and one of the first steps towards total abolition in the United States as a whole. While not a perfect solution, it was important.
The Gradual Abolition of Slavery act did a great deal to end slavery, because it put the events in motion that ultimately ended slavery. The Act let the American people know where the federal government stood on the issue. It let the public know that the federal government would not back down, and it set the political tone for ultimately freeing the slaves.
Trying to abolish slavery outright was very difficult, and getting a bill passed for the abolition of slavery that was completely unanimous would have been impossible. An act was submitted before Pennsylvania legislature that suggested a gradual freeing of slaves over a span of almost 30 years. It outlined an idea that, if it worked, would have gradually freed slaves and given plantation owners and slaveholders the chance to slowly adapt.