To-morrow, and to-morrow, and to-morrow,

creeps in this petty pace from day to day,

to the last syllable of recorded time;

and all our yesterdays have lighted fools

the way to dusty death. Out, out, brief candle!

Life's but a walking shadow, a poor player,

that struts and frets his hour upon the stage,

and then is heard no more. It is a tale

told by an idiot, full of sound and fury,

signifying nothing.

These dark, despairing words are of course from Act V of Shakespeare's classic tragedy, "Macbeth." Why quote them here? Because lately I've also been thinking about three "to-morrows." And I have become convinced that whatever meaning and purpose we may find as we strut and fret, our hour on the stage is determined by which of those three tomorrows we choose to live by.

What do I mean by which tomorrow? Consider the following: a short-term tomorrow, a long-term tomorrow and what I'll call a very, very long-term tomorrow.

The short-term tomorrow is just that - tomorrow. It's a tomorrow you must concern yourself with to put dinner on the table each night and to get to the office on time. But having too heavy a focus on short-term tomorrow is unlikely to lead to a rewarding or meaningful life. In fact, I would say the exact opposite is true. Consider Macbeth. When we first meet him, he has a bright to-morrow, slated for promotion you might say. But he (and his wife) get seduced by ambition and go for short-term rewards. Macbeth's path leads upwards for a time, but ultimately ends in despair - his life becomes a tale told by an idiot, signifying nothing.

Now, I am fairly confident that few view Macbeth as a role model. Nevertheless, the world is full of Macbeths. Time and again people - often those we expect more of - choose to take shortcuts, betray our trust and act for personal gain. Perhaps without even realizing it, these people come to use short-term tomorrow as their guidepost. It's a cautionary tale.

A far more rewarding path embraces the long-term tomorrow, a tomorrow that takes a longer view, considers how one's actions impact the world today and in the future. It's a path that compels one to become engaged with the great issues of one's time and to take responsibility for the consequences of one's actions.

This is easier said than done. When one looks at the world today - the environment, the economy, poverty, wars - the future can be bleak. It is easy to despair, give up and cash in.

The problem, of course, is that we all can't do that. In about 40 years, there will be some nine billion people on Earth.

Where will the resources come from to provide for these people? How will we maintain the ecosystems and natural resources upon which we all depend? What will happen to our children and grandchildren? What will happen to all of us?

In truth, I have no idea. But I do have hope.

I recently read a fascinating book called "The Beginning of Infinity" by David Deutsch, an Oxford University quantum physicist. Deutsch's essential argument is that humans - as intelligent beings who have learned to harness the power of the scientific method of inquiry, conjecture, and testing - have unlimited possibilities. At some point, he predicts, if we are successful we will become unencumbered by planet Earth, no longer dependent upon nature for food, water, fiber and energy.

Who knows? Deutsch may prove to be right, in some very distant tomorrow. And our efforts today might be moving us in the direction of that unlimited progress. In the meantime, we have long-term tomorrow to worry about.

In the end it's a juggling act with all three tomorrows. You have to have short-term tomorrow in the mix, but keep it moving. Hold tighter to long-term tomorrow. And when things get tough, when it seems like there's no way to keep all the balls in the air, get some perspective by considering very, very long-term tomorrow.

At the end of the Broadway play called "Master Class," the great opera diva Maria Callas says, reflecting on her life: "I am certain that what we do matters."

I, too, am certain.

If we turn our energies to engagement with the great issues of our day, to making the world a better place, we will likely find ourselves immersed in an extraordinarily rewarding life. A life that may very well be filled with sound and fury, but also with meaning.