Within an hour after the attack in Boston on Monday, many out-of-town friends texted or e-mailed to check in. Yes, we were okay. Okay, but desperately sad.

Soon enough it became all too plain that this was an intentional act. Someone decided to find yet another way to wreak mayhem against innocents to right some perceived wrong, or achieve some sort of twisted revenge. In time we will know who it was, and what they were thinking. But we will not be able to comprehend why.

Remember that it's not an accident that the Boston Marathon always takes place, as the president reminded us, on the third Monday of April -- Patriots' Day, in the Commonwealth. It is a day intended to commemorate the beginning of a long struggle that eventually secured the independence of our nation, and made possible the creation of a grand experiment -- a self-governing democracy, ordered by the rule of law, and based on the seemingly outlandish proposition that all people deserve to be regarded with an essential equality.

There is no greater threat to the survival of such a remarkable nation than the erosion of trust between the people and communities that comprise it. Those who design these inhuman attacks know this; and it is exactly their hope that the fear and dread caused by their handiwork will bring about that result. Sadly, the course of our history since the terrible attacks of September 11, 2001 would seem to bear them out. Consider the increasing polarization of our political discourse, the deepening divides that estrange neighbor from neighbor, class from class, faith from faith.

We must now resolve to do better. We must take this moment as a call to rededicate ourselves to the principle that the bonds that unite us -- our common desire to live in peace, our common right to expect equal treatment from our government and each other, our common hope to “secure the Blessings of Liberty to ourselves and our Posterity” -- deserve more of our work, more of our selves, more of the investment of our substance than the differences, real and imagined between us.

Millions of people around the world live in fear every hour of every day, and look to us in hope. A disappointed, miserable few look to us in envy, and seek to destroy this last, best hope of earth by turning us against each other. Too often, we have made their job easier.

If they are not to succeed, we must attend to the health of the hopes we share. Those who died at the hands of this madness were standing along Boylston Street only because they came with joy to witness one of the greatest of all human feats. Their race has now been won. Our marathon continues. Let us press on.