We know from sheer logic that it is important that there be a purpose for life. Man has asked for his entire existence, "Why am I here? What is the meaning of life?" Atheists, if they are honest, have to admit that the answer is "whatever you want it to be" which, in its final analysis, is both "nothing" and "everything" where "everything" is singularly small. They might have something like "personal fulfillment" or the like, but in the end it has little weight. No, if there is to be grand meaning to life, it must have a grand origin, not an "I live so I matter" start.
The fact, however, that even the honest atheist builds a purpose for life, even if it is a merely individual one, shows that purpose is indeed important. In the end, whether or not you like Warren or his book, we humans do need to have purpose-driven lives. Now, to most their purpose is tiny. More money, more power, a better car or house, that spouse to fulfill me, the list goes on and on into shallow oblivion. Others build grander schemes for themselves -- "become president" or "cure cancer" or "world peace". Because we all need a purpose. But if we are created by God for a purpose, it would seem to me that 1) there is indeed a purpose for our existence, 2) we should find out what that purpose is, and 3) we should live our lives according to that purpose. If we are to live a purpose-driven life, what is that purpose?
We like to think that we are our own. You'll commonly hear, "I am my own man." But it's not the case. We are creatures, created beings owned by a Creator. He made us for a purpose. Thus, it would stand to reason that our purpose ought to be whatever His purpose is. What is that? The purpose of life is clear -- God's purpose (Eph 1:11) which is God's glory (1 Cor 10:31; Isa 43:7). At its core, a purpose-driven life must be aimed primarily and continually at "the praise of His glory" (Eph 1:6,12,14). Our failure is that we "fall short of His glory" (Rom 3:23). The command is "whatever you do, do all to the glory of God." (1 Cor 10:31)
Living for His glory may take many forms. There is obedience without legalism, but as worship. There is sacrifice (Rom 12:1). There is serving in various ways and shapes that God has ordained and explained. The appearance is not always the same (1 Cor 12:7,11; 1 Cor 12:14-25). It takes many forms with various facets, but always one purpose. This runs completely counter to the standard human perspective which says, "I get to make my own purpose." The question we are told to ask ourselves is "What do you want to do?" when the question ought to be "How can I glorify God?"
If we were built for a purpose and fail to aim toward it, we are missing the mark, spinning our wheels, failing to live up to our reason for living. The world tells us that our purpose is personal satisfaction. Reach for the stars. Live the dream. Don't let anyone get in your way. They are wrong in their emphasis, but right that we need to have purpose for our lives. What we need is to recognize our Maker's purpose for our lives and engage that purpose. The Reformers had a Latin phrase for it: soli Deo gloria -- Glory to God alone -- the divine purpose for His creation.
Not to us, O LORD, not to us, but to Your name give glory, for the sake of Your steadfast love and Your faithfulness! (Psa 115:1)