He couldn't stand it then and it makes him furious when someone says it now.
Satan thoroughly despises humans, but above all he hates those who recite a particular prayer from the depths of their heart. It is a prayer the directly contradicts what he proclaimed to God when he led a rebellion against the heavenly hosts.
There are many traditions surrounding Satan’s rebellion against God at the beginning of time. One of them relates the devil’s outright refusal to serve God. Various spiritual writers have interpreted the following passage in Jeremiah to be a perfect description of Lucifer’s fall from Heaven.
For long ago you broke your yoke
and burst your bonds;
and you said, “I will not serve.” (Jeremiah 2:20)
Writer John Milton wrote a famous poem in the 17th century called Paradise Lost, and in it he assigns that particular phrase, “I will not serve” to Satan himself. He uses the Latin non serviam to summarize Satan’s stark disobedience.
It should come as no surprise that the prayer that Satan abhors the most is the opposite phrase, “I will serve” (serviam in Latin). St. Josemaria Escriva meditates on this “flipping the coin” in The Way.
The non serviam of Satan has been too fruitful. Don’t you feel the generous urge to express your daily desire for prayer and work with a serviam — I will serve you, I will be faithful! — which will surpass in fruitfulness that cry of revolt?
Many people around the world say this short and simple prayer of Serviam (“I will serve”) at the start of each day, pledging their life to God. It is a prayer of the heart, one that stands in stark contrast to the non serviam (“I will not serve”) of Satan.
It is a similar prayer to the “Jesus Prayer” that Eastern Christians are familiar with and can be prayed over and over again throughout the day. It is even a prayer that can be said when faced with a temptation, adding, “I will serve God.”
The Blessed Virgin Mary said a similar phrase at the Annunciation when she said, “Behold, I am the handmaid of the Lord; let it be to me according to your word.” (Luke 1:38) The primary phrase of her humble obedience in Latin is fiat, or in English “let it be done.” For this reason Satan hates the Blessed Mother, as he revealed to Fr. Gabriele Amorth in a dialogue he had with a demon.
Father Amorth: “What are the virtues of the Madonna that make you angriest?”
Demon: “She makes me angry because she is the humblest of all creatures, and because I am the proudest; because she is the purest of all creatures, and I am not; because, of all creatures, she is the most obedient to God, and I am a rebel!”
Being a servant of God is the true goal of the Christian life, as Jesus himself explains in the Gospel of John.
If any one serves me, he must follow me; and where I am, there shall my servant be also; if any one serves me, the Father will honor him. (John 12:26)
The next time you are looking for a prayer to show your steadfast loyalty to God and trust in his divine providence, simply say “I will serve.”