Why do birds fly?

My answer would be that "Birds are designed to fly."

However, the offspring of a bird does not start out flying. It has to let its wings develop fully and get the hang of them with much flapping exercises while watching on the sideline as its parents take their daily flights, before launching-off on its own maiden flight.

Likewise, we need to know what we are designed for. The book of Isaiah in the Holy Bible says to the effect that they that wait on the LORD (their Creator), shall mount up with wings like the eagles, run and not be weary, walk and not faint. It's not waiting for something to happen, but waiting upon our Maker to commune with us. The answer for both our general and specific designs rest with the Immortal One who made us all.

Thus, we need to draw near and get to know Him (so that we can know what He already knows about us!). No wonder in the book of Psalm (chapter 46 verse 10 - New International Version), we are urged by the word of God to: "Be still, and know that I am God; I will be exalted among the nations, I will be exalted in the earth."

That said, a bird cannot fly if its wings are broken. Likewise for us we are to: "Hold fast to dreams, For if dreams die, Life is a broken-winged bird that cannot fly, Hold fast to dreams, For if dreams go, Life is a barren field, Frozen with snow." -- Langston Hughes

We must learn to fly by the by. It's already built-in. Even if our wings are broken, they can mend and be healed so that we can soar to the sky, again. Heads up, we aren't grounded chickens!