"The two most important days in your life are the day you are born and the day you find out why."
What is the purpose of life? I think that we even ask this question, shows the difference between humans and animals. Who knows what animals think - but I dare to doubt that animals think about philosophical issues as much as we humans do, because they simply enjoy the here and now - their existence. However, it is very important that a person asks such a question - it shows that we humans are more, have more within us.
Overall I think our ultimate purpose is to find the "tree of life" thus the path to eternal life for our soul as it is promised to us by God. After God send Adam and Eve away from Garden Eden he sent them to earth to find through the material life the way back to him. We need to earn our eternal life and God gave us clear rules in the 10 commandments and scriptures on how to go about that. Jesus in my view is this tree of life for us, as he mentions that no one will go through paradise except through him. He showed us Gods endless mercy. Doing good, following the commandments and thus finding the way back to God and eternal life is in my view the purpose of all humans on this planet.
In addition, I personally believe that the "why"-question and the purpose of life also has an individual angle. Everyone has their own personal purpose and task to fulfill their learning units here on earth. That makes the whole thing very difficult for some. From childhood, many are used to being told everything including what is right and wrong, what we should and should not do. What our environment thinks about us with family, acquaintances, society etc. telling us what is good for us. And then suddenly there is the question of why, of the whole meaning behind it that goes deeper - and then there is a silence of the outer world. Nobody says to us: "The meaning of your life is to paint beautiful pictures and make people happy with them" - or "to become a good carpenter and to create beautiful wooden furniture which many will enjoy for a long time", or "to become a salesperson to advise people well so that they get exactly what they are looking for and need" etc. as this is just a profession but not the whole purpose right? No - we have to find out for ourselves why we are here on earth, what our mission is. For many, this is too troublesome, those prefer to follow what is indirectly imposed on them by society and their environment. Or we plunge into sensual desires and distractions and spend hours and hours in front of the television where we can indulge without doing anything or in front of the computer where Facebook and Co. let's us find out about others lives instead of meeting them in person.
Finding out what the personal path of life is, requires effort, going deep into ourselves and learn use our intuition. I find Paolo Coelho's book "The Alchemist" excellent - it tells the story of a shepherd having a dream and getting involved in finding a treasure. He breaks out of his comfort zone, develops himself incredibly, follows the signs laid out for him and learns the lessons life is offering and thus finds the purpose of life. A very nice illustration - so let's go, let's find the personal meaning of life that our Creator intended for each of us. With leaving our comfort zone, using our intuition and paying attention to the signs on our path God has laid for us, we will be able to find our very personal purpose of life.