Eight years ago this morning, terrorists commandeered two passenger jets that took off from Logan Airport and flew them into the World Trade Center. That attack forever changed the nation’s mindset. But for loved ones of the 3,000 people who were killed that day - including more than 200 with ties to Massachusetts - this date will always represent a personal tragedy as well. Many victims’ families, in conjunction with community-service groups, are asking their fellow citizens to commemorate that grievous loss by giving more of themselves. Fittingly, President Obama signed legislation earlier this year designating the anniversary of the attacks as a “national day of service and remembrance.’’ Eight years on, Sept. 11 remains both a day for somber contemplation and a reminder of the obligations all Americans have to one another.