"Teach us to number our days, that we may gain a heart of wisdom." (Psalms. 90:12)
Have you actually tried numbering your days, literally? It's a little depressing, but worth doing.
Let's take 60 years as an optimistic average remaining life expectancy for the people reading this this post. This is actually a good estimate if you're around 20 years old. If you're older, naturally your remaining life expectancy will be correspondingly shorter. 60 years converts to roughly 21,900 days. Is this a large number?
It is less than the number of verses in the Bible, which contains over 31,000 verses. If you spent every day meditating on a single verse of the Bible, you'd die before you finished.
It is less than the number of friends of friends you have, assuming you have 150 friends who each have 150 more friends. A quick browsing through Facebook indicates that this is actually a low estimate, even after taking mutual friends into account. If you spent each day being introduced to a new friend of a friend, you would die before you finished.
It is likely to be less than the number of pennies you have in your bank account. (You have my sympathy if that's not the case) And that's a number that nobody thinks is particularly large.
Imagine a countdown of days, starting from 21,900, numbering the days left until you die. Now, consider the things you want to achieve in life. Do you want to get an advanced degree? That takes somewhere between 300 to 3,000 days. Do you want to travel the world? Let's make that a brisk 80 days, plus perhaps another 500 to accumulate the funds and the vacation time. Do you want to write a book, or go on a significant missions trip? Another 300-400 days at least. How about raising a family? Just getting married probably takes something like 600 days, and another 7000 days or so for your children to reach maturity.
But what if you want to tackle something big and extraordinary? What if you want to change the world? What if you want to hear, "well done, good and faithful servant"? I obviously can't give an upper bound to such things, but to do anything significant you probably have to be really good at something, and that's said to take around ten thousand hours of intentional practice. That's perhaps 2,000 days, just for the ability to get started.
Ah, but what if you're already accomplished, and have many of these experiences under your belt? Then you know that the sand in the hourglass falls with increasing gravity. You probably have less than 21,900 days in this case, and you're able to see, because of your increased understanding, more specific things that remains to be done, more work that you can realistically tackle - and it's all the more clear to you that you cannot do everything that you want to.
What if you're younger, and have more days left in your life? Then you should know that not all days are created equal. Conventional wisdom says that your younger days are more valuable than your days in old age. They influence you more, they're perceived to be more eventful, and they determine the course of your remaining days. Thus the Teacher counsels us to remember the Creator in the days of our youth. Yes, I know this is probably something you've heard a million times. I have, too. But it's often repeated because it's true.
Besides, even if you have more days left in your life - say that you bump up the number of days to a rather unlikely 30,000 - that doesn't change the basic point. Even taking into account that you can do some things simultaneously, even if you already have some experiences, even if you have more days than some other people, anything of significance requires hundreds to thousands of days, and you only have, at most, tens of thousands available to you.
Does this make you nervous? Does it feel like you're suddenly under a terrible constraint? But nothing has changed; you simply see the unchanged situation more clearly.
As for myself, it does makes me nervous. As someone who's let too many of the best days of my life slip through my hands, as someone old enough to appreciate that I will not be able to do everything I want to, as someone frequently guilty of sloth - this post has been difficult for me to write. I was going to add to this post the various ways that people waste time to ratchet up the rhetorical pressure (video games, etc), but there's only so much my own conscience can bear.
Now, then, how should we live?
In some sense I live like I'm going to live forever. There is some truth to that, of course - I am in fact going to live forever. But the only way that I understand “forever” is through the “now”. Thus the only way I can justifiably act like I'm going to live forever is by acting like now is the only time in existence.
Thus it seems to me that there are two wise ways to think about my time. One is to remember that we have a fewer than a few tens of thousands of days to live, and to live to make them count. The other is to live like we'll live forever, remembering that the only aspect of eternity that's available to us is the present. What I do in the present is how I've spent the eternity available to me.
The second way seems to me the deeper way of seeing things, but using both approaches is probably best. Of course, we often live like we have an infinite number of days in the future remaining ahead of us, which we certainly do not have.
May the Lord God grant you and me a heart of wisdom, so that we can make the most of each moment of eternity.