Our greatest gift is a free will. We can choose to do God's will which brings lasting joy, or to follow our passions seeking only temporary pleasures. One leads us to union with Him and the other.....
Elder Macarius says,
We must keep our arms polished and use them courageously in our two unceasing wars: our offensive war, the fight to understand and follow His law; and our defensive war, our resolution never to succumb to that which is contrary to His law; the law being nothing but His expressed will.It is when we deviate from His law that we find ourselves in this unending striving for things that only bring temporary satisfaction.
The Elder says,
For, alas, no sooner does a man break God's law, than he is spiritually punished: having lost grace, he eats away his heart in vain longings, endeavoring all the while to choose for himself the best of many equally bad things. these longings and endeavors deflect his attention away from his real good, and dim his intelligence. Soon, having become a slave to his passions, he can no linger resist their lure; then the mead of pleasure changes to the sting of retribution.Stick to the principles and disciplines of an Orthodox Way of Life and you will be guided to make the right choices.
Reference: Russian Letters of Spiritual Direction, p 77