The Halifax Explosion caused people in both Halifax and Dartmouth to band together to help one another. Some children lost their parents and entire families. Many were blinded from broken glass and other debris. Everyone worked together to rebuild the parts of the city that were impacted. While only parts of the cities faced destroyed homes, many areas near the Basin and Harbour had broken windows. This was a problem because the explosion happened in December, a time of the year that is bitterly cold in Nova Scotia.
As others mentioned, the Bostonians were the first to respond with aid. It is because of this that many Haligonians are fans of Boston sports teams today. As previously mentioned, the Nova Scotians send a Christmas tree to Boston each year.
The Halifax explosion is continually remembered in Canada as the deadliest wartime accident on Canadian soil. I grew up in Concord where the Port Chicago disaster is also memorialized every year and it is still very real to some of the old timers who live there.
I would also argue that it is still very important because the investigation that was launched afterwards helped improve safety in harbors all over the western world. Some of the safety precautions prescribed after the disaster were actually used at Pearl Harbor in 1941, especially the clean-up and repair procedures that were standardized.
The explosion in Halifax, Nova Scotia in December 1917 was caused by a munitions ship leaving for Europe to supply the British during World War I. About 2,000 people were killed and the harbor was destroyed; the anchor of the ship was found 2 and half miles inland, where I'm told it's been left where it landed as a memorial.
Boston was the first city to respond with aid, being just a day's sail from Halifax, and at the time, the preeminent medical authority in the US, as well as one of the busiest ports. So off went shiploads of supplies, disaster relief, and medical personnel.
The people of Halifax were so grateful for the aid that a few years later, after they had gotten back up on their feet, they sent a 100 foot pine tree to Boston at Christmastime as a thank you.
...and they've been doing it every year since.
The True Meaning of Christmas? All I know is that there's a nearly century-old thank-you tradition between the peoples of Boston and Halifax, and I get to enjoy their Christmas tree every year.
Wouldn't it be because of the way in which the neighborhoods that were destroyed in the blast were rebuilt? As I understand it, the neighborhoods were rebuilt in a much nicer way that allowed the relatively poor people of those areas to enjoy a more pleasant environment than they had before.