To begin to answer to the question below, let me take a short excursion into metaphysics.
When we examine “Being” philosophically, we see that the first crucial divide is the one between Creator and creatures. On the one hand, Absolute Being, Infinite Perfection, on the other: metaphysical dependence and contingency. No creature can account for its own existence; it was God’s gift. The second most radical divide is between personal and non-personal being. On one side, we have the Absolute Person, God, but also angels and human beings. On the other, all impersonal creatures: animals, plans, rocks and minerals.
I recall once hearing Cardinal Schonborne give a talk on evolution in which he mentioned that the difference between a chimpanzee’s DNA and ours is minimal, but this “insignificant” difference is the abyss between someone who can say I, somethone who can pray, someone who can love another not because of needs, but because of his beauty and goodness. Because man has an immortal soul, every single organ of his body is elevated to a totally different level. This is why an eagle’s superb eye sight does not perceive and therefore cannot contemplate beauty. This is why the amazing sensitivity of dogs to “decibels” does not enable them to be moved to tears by sublime music.
When God created Adam and Eve, He made them kings of creation. They were masters over material nature. Nature was to feed them, and provide for their needs. All impersonal creatures were given to serve human ends (which of course, does not mean that this ownership could not be abused—something which happened, alas, after original sin).
Because of his dignity as a person, man can never be used as a mere instrument, a mere tool whose purpose is to “serve” others, as if he were a lemon that can be squeezed and its rind discarded. This is so true that God respects human freedom—taking the “risk” that men might abuse this freedom.
This was Kant’s great insight when he defined a person as a being who is an end in himself, never to be used as a mere means.
But from this, we should not draw the conclusion that man is his own end. Man, being an imperfect creature cannot be his own “fulfillment”. To be person is to be called to be in communion with others. Animals “flock” together. Man is called to love—which is not an instinct, but a sign of his nobility and capacity to transcend himself. He is called, primarily, to be in communion with His Creator, through adoration, praise, gratitude. He is called upon to “love his neighbors”—persons like himself made to God’s image and existence. By transcending himself, he fully finds himself.
To suppose that man “does not need” anything beside his own being, is to forget that he is but a frail and imperfect creature. “Thou hast made us for Thyself, and our hearts are restless till they rest in Thee.” (St. Augustine, Confession I, 1)