Consider this statement from St. John Chrysostom:
It is necessary most of all for one who is fasting to curb anger, to accustom himself to meekness and condescension, to have a contrite heart, to repulse impure thoughts and desires, to examine his conscience, to put his mind to the test and to verify what good has been done by us in this or any other week, and which deficiency we have corrected in ourselves in the present week. This is true fasting.
Apply this same mindset to trials we face in life. The reward isn’t just in what we get in heaven, but in the intimacy we achieve with God through the trials of life. Difficulty situations and suffering force our hand to let go of the things over which we have no control in this world to focus on God alone. The other choice is to cling to the things of the world which will only cause us more pain and distance from God.
That is why we fast and pray. Fasting is but one practice that trains us through self-discipline so that when trials do face us, we have the spiritual strength to endure.