".... Lavan was informed that Yaakov had fled. He took his relatives with him and pursued him" [Vayeitze 31:22,23]
The Maggid of Mezritch taught: "Yaakov had left behind letters from the Torah which he had not yet extracted from Lavan. This is why Lavan pursued him - to give him the letters which remained with him. An entire chapter was added to the Torah by these letters." [Ohr Hame'ir, beg. Parshas Vayeitzei, see Ohr HaTorah vol 5, p.869a]
The "letters of the Torah" which Yaakov left behind were "sparks" of holiness. In fact, Yaakov had spent twenty years in Lavan's house extracting whatever sparks of holiness he could find there, and when the process was complete, he left. At least he thought it was complete....
In truth, however, Yaakov had left some sparks behind, so Lavan chased Yaakov to give them to him.
Why did Yaakov leave sparks behind?
Chassidic teachings explain that, while most of a person's achievements in life come through his own conscious efforts, there are some "super-conscious" achievements that are so lofty they cannot occur intentionally. So, while we are usually the ones that choose our own paths in life - to find the sparks which we are destined to elevate - sometimes our "sparks" pursue us, because they are too sublime to be "extracted" solely by our own endeavors.
Source: Based on Likutei Sichos of the Lubavitcher Rebbe, Gutnick Chumash