His work in Game 4 was largely overshaddowed by the rightful lead story work of the bench, but if Pierce doesn't start off aggressive and finish strong, we don't win that game. Which is why he's the Captian and why he's gotta keep doing work to get the job done.
Paul Pierce certainly isn't the fastest player in these finals. He's strong, but not overpowering. He's a good shooter, but he needs time and space to get a deep jumper off. More than any other "superstar" in these finals, Pierce is capable of being a relative non-factor for long stretches of time. Pierce likely knows all of that. He also knows that if he can get himself his second ring and the Celtics their 18th banner, it won't matter whether he averaged 30 points per game or 3 points per game in the finals.
With two Hall-Of-Famers and one other all-star in the Boston starting lineup, Pierce's job isn't to be the best player on the floor. His job is to grab that one extra loose ball, draw that one extra foul, make that one extra step-back that the Celtics his team needs him to get. On Thursday night, Pierce was able to do just that. If he can do just enough two more times, he'll officially enter his name into Celtics lore.
I'd argue that he's already in there, but he would certainly take his place in the higher rung of lore if we win 2 more games.