You can do it, or you can be it. I mean that the things we do seem to have two different kinds of status: there are things to do, which are at arm's length from our identities, and things to be, which are actually part of how we define and describe ourselves. Think of someone who says "I'm an actress - but right now I'm waiting tables to support myself." An actress is something to be; waiting tables is something to do. It's possible to imagine someone saying the opposite: "I'm a waitress - but right now I'm doing some acting to get my name out in the community." That would have a different meaning, though, and it would be a more suprising meaning. The same actions can be things to do or things to be, we see a difference between those kinds of things, and some actions are expected to be more likely one kind or the other even though they can fall into either category.
Looking at the two waitress/actress statements suggests one of the important differences between things to be and things to do: you usually do something for a specific reason (a rationale is given in each sentence), whereas something to be is its own reason. There are also some linguistic clues: things to do tend to be verbs ("waiting," "acting"), whereas things to be tend to be nouns and adjectives ("actress," "waiter"). There are subtleties to that, though. Compare "I will cook" (verb, future tense), "I am cooking" (verb, present participle with "to be"), "I cook" (verb, simple present tense), and "I am a cook" (noun with "to be"). It seems that "I will cook" and "I am cooking" are both talking about something to do; they're not talking about the identity and definition of the speaker, just his or her actions. Even though the present participle is used with the verb "to be," that's just an accident of the grammar and "I am cooking" is not really talking about a state of existence; the person who says that isn't necessarily a cook.
The statement "I cook" is describing something deeper. That's the simple present tense, which in English refers to repeated and typical actions. The speaker isn't just cooking right now or on some specific occasion, but describing the general way things are - cooking is part of the description of that person. That's something to be even if it's described using a verb. Saying "I am a cook" is even more definitely a description: a cook is both grammatically and conceptually something to be, not just something to do.
To do is to be - Socrates
To be is to do - Plato
Do-be-do-be-do - Sinatra
Yabba dabba doo - Flintstone
There's a logical implication between these two kinds of things but it only goes strongly in one direction. If you are a skier, that's something to be. It means that you pretty definitely do go skiing sometimes. If you never ski then it's hard to claim that you really are a skier. To be implies to do. However, the converse isn't necessarily true. Lots of people do go skiing sometimes without really being well-described by the noun "skier." For instance, where I grew up a class ski trip was the traditional yearly high school outing. Many of those kids never did ski on any other occasions; I'd contend that they weren't skiers. For people like that it was something to do without being something to be. That's a sort of soft non-implication, though. If you ski enough, it seems that you are a skier. To do does imply to be after all, if it's typical, frequent, habitual, or important.
Suppose you want to hire someone for a job that involves computer programming in C++. Do you want to hire someone who can program in C++ - which is something to do? Or do you want to hire someone who is a C++ programmer - which is something to be? If you think there is a difference that matters, and you get both kinds of applicants, how will you know the difference between them?
I found some interesting similar ideas by searching Google for the "do be do be do" quote, but nothing that formulated it exactly as I'm doing here. This is actually an introduction for some other things I'm planning to post later, but I wanted to make it a separate page because I've generally found readers and commentators reluctant to address generalities if I mention the specific examples of interest to me; maybe if I don't tell you the specific applications yet I can get some contributions on my own terms. The Colour concept is somewhat related in that it's talking about a deeper more abstract attribute that goes beyond the directly observable; I think there's more to being than just doing.
Another thing I've been thinking about is Aristotle's idea of "substance" by way of Christian transubstantiation which seems to rest on it. In that theory you've got the observable properties of things, which are called "accidents" and include statements like "this is wafers and wine," and the unobservable deep abstract nature of things, which is called the "substance," and includes statements like "this is the body and blood of Christ." Some people believe both those statements can be true at once because they're talking about different things. Others don't believe that. Substance versus accidents isn't exactly the same as things to be versus things to do, and I'm not taking a position on the entire theory of substance nor on transubstantiation here; but I'll say again, I do believe (and I am a believer) that there's a meaningful and important difference between things a human can do and things a human can be.
Suppose you're looking on those meet-new-people Web sites for someone who shares your interest in roller skating. Do you want to meet someone who is willing to skate - which is something to do? Or do you want to meet someone who is a skater - which is something to be? If you think there is a difference that matters, and there are profiles of both kinds of people on the site, how will you know the difference between them? How will you write your own profile to solicit responses from one kind in preference to the other?