The meaning and purpose of life aren’t all that easy to figure out. To answer the question involves answering other questions: What does it mean to have meaning and purpose? How do you determine what that is? Do you determine your own meaning? Can you combine what you think is your own purpose with the purpose that someone else might have for you? There are lots of questions and no easy answers. Well, let me correct myself. There is an easy answer.
What Does the Bible say is the purpose of our lives?
"Everyone who is called by My name, And whom I have created for My glory, Whom I have formed, even whom I have made," (Isaiah 43:7).
According to the Bible, our purpose, the reason we are here, is for God's glory. In other words, our purpose is to praise God, worship him, to proclaim his greatness, and to accomplish his will. This is what glorifies him. Therefore, in this, we find that God has given us a reason for our existence, a meaning for our existence. We were created by him, according to his desire, and our lives are to be lived for him so that we might accomplish what he has for us to do. When we trust the one who has made us, who works all things after the counsel of his will (Ephesians 1:11), then we are able to live a life of purpose. How the particulars of that purpose are expressed is up to the individual.
Is there a purpose in trials?
What if our lives are difficult and things go wrong? Are our failures and hardships for the glory of God, too? Yes, they are. We often thank God and praise his name when things go well, but we often turn our backs on him and complain when things are difficult. Sometimes our appreciation and trust in God become conditioned on how well things are going for us. Ultimately, this is self-centered immaturity. Even though things can go wrong in our lives, the ultimate reason we are here is to glorify God -- even through the difficulties. We do this by praising him and trusting him through difficult times.
Within this attempt to glorify God -- in all things -- we can then determine the particular meaning of our life that God has for us specifically. In Christianity, we are free to pursue God in all areas of our lives. For example, we are free to glorify God by being a doctor, a lawyer, a mechanic, a housewife, a father, a mother, a minister, an accountant, etc. If the ultimate goal in life is to bring glory to God, then we can do that by being the best at what we do in the various callings of life. So, as the Bible says, "...whatever you do, do all to the glory of God," (1 Cor. 10:31).
I want to determine my own purpose
There are those who will not like this. There are those who will deny that God has made us. For them, they want to determine their own purpose. They must decide for themselves what is meaningful to them. They want their independence. They want to proclaim what is good and bad in their own hearts and determine their purpose based on their desires. But the problem is that this becomes self-serving. When we do what we think is right in our own eyes, we often make mistakes -- especially when we deny God. When a child says "I want, I want, I want," he is showing his immaturity and self-centeredness. Adults become other-centered as is demonstrated by the sacrifices involved in parenthood and marriage. As we grow older, we realize the value in considering the interests of others. "Do not merely look out for your own personal interests, but also for the interests of others," (Phil. 2:4). In this, we learn that purpose is best defined not by selfish desires but by the ability to love and consider others more important. This carries over to receiving a purpose from God. If we are selfish and want to determine our own purpose, then how is that truly loving? After all, if love is other-centered then shouldn't we love God, center our lives on him, and humble ourselves before him in his wisdom and trust what he desires for us? Think about it. He knows infinitely more than we do, and by trusting him we can discover the ultimate purpose of our lives. It makes sense.
Moralism is simply doing what is good for goodness sake. An atheist can do that, but for those who claim to be Christians, our purpose is not our own glory. The meaning of our lives is to bring glory to God (Isa. 43:7). Unbelievers do not know God. Therefore, they can only be moralistic in their self-determination of meaning and purpose. That is, they have no objective moral standard that exists outside of themselves, and so they have no way of knowing what their ultimate purpose really is. They will then, at best, adopt a kind of moralism, a goodness that is relative to the preferences and situation and live a kind of conditional love. In that way, they cannot know what real goodness is. And without knowing what truly is good, how can they truly have a good purpose in their lives?
For the Christian
The right thing to do is bring glory to God because there is no one greater who is worthy of trust, adoration, and worship. Therefore, for the Christian, we are to live to bring glory to God. How we do that is through prayer and study of His Word, the Bible, so that we might better know what He has for us.