Prayer changes us not God. By asking for what we need, even though God already knows what we need, we establish and nurture the deepest roots of our relationship with our Father: humility. By asking for what we need and receiving His gifts with thanksgiving, we feed, strengthen, and grow our obedience to His will and thrive by participating more intensely in His divine nature.
And this is why the Word was made flesh: so that we might come to the Father perfect as He himself is perfect. Isaiah reports the Lord saying, "[My word] shall not return to me void, but shall do my will, achieving the end for which I sent it." He sent His word among us with a purpose. Not to frighten us with threats of punishment, or beat us into submission, or bribe us with promises of fabulous wealth. He sent His word among us to love us and to return us to Him in love. We do not have to consult drugged-out oracles or read the entrails of sacrificed animals to know our Father's will for us. We pray, "Your will be done. . ." and give Him thanks and praise. His word will achieve its end. And that end is our salvation.