If you agree that man and woman were created by God, and are not just some biological accident occurring in the process of purposeless evolution, the next question to ask is why did God create humans?
God created man and woman out of love so that he could make them eternally happy. It then follows to ask the question: What is eternal happiness?
Eternal happiness is the possession of the greatest Love that exists, and to be possessed by it; to be in union with it. And that Love is nothing but the infinitely perfect God, our creator. Eternal happiness is not reached here on earth but only in heaven.
So what am I doing here on earth?
Earth is where I begin my journey of life; a life that continues on into eternity. It's where I grow, learn, and discover things. And it is here on this earth that the necessary foundation for the happiness of heaven is laid. The foundation is laid by learning all I can about God (for I can't love what I don't know), loving him, and proving my love for him.
This foundation is a must if eternal happiness is to be achieved. Because if there is no beginning of love in my heart for God here on earth, then there can be no realization of that love in eternity. If after a long time away, I'd be going home to someone I love dearly, then finally home and united with that loved one, I'd be so happy. But if I went home and met someone I did not know or did not love, what happiness would there be?
The happiness of heaven is the final and complete possession of the God we have desired and loved weakly at a distance. And if it is to be our destiny—to be eternally united with God in love—then it follows that we must begin to love God here in this life.
Ref: The Faith Explained by Leo J. Trese