"Allah has favoured Friday over all other days, the month of Ramadhan over all other months, and Laylatul Qadr over all other nights." Prophet Muhammad (pbuh)
This name was used for Laylatul Qadr because Allah determines what will happen for everyone in the entire next year. The "Qadr" in this sense means destiny. According to Al Qummi's Tafsir, as explained on p. 432 of its second volume, such destiny includes life and death, sustenance, abundance of crops or famine and everything good or bad. This means that Allah determines in this night each and every event to occur during the next year to any and all of His creation.
Sulayman al- Marzawi asked Imam Ali Ar Ridha (pbuh)
"Could you please tell us why Suratul Qadr was revealed?"
"O Sulayman! Laylatul Qadr is the night when Allah decrees what will take place from one year to another of life or death, good or evil, regarding sustenance and whatever He then decrees is sure destiny."
“Whoever spends Laylatul Qadr in ibada to his/her Rabb will have all his/her sins forgiven even if they had numbered as many as the stars in the heavens, the weight of the mountains, or the measures of the seas.” Imam Muhammad Al Baqir (pbuh)
"The Holy Qur'an was revealed as a whole during the month of Ramadan at the Ancient House (the Ka'ba), then from there it was revealed along the span of (more than) twenty years." Imam Sadiq (pbuh)
"The Books of Ibrahim (pbuh) were revealed on the first night of the month of Ramadan; the Torah was revealed on the sixth of the month of Ramadan; the Gospel (Injil) was revealed on the thirteenth of the month of Ramadan; the Psalms (Zabur) were revealed on the eighteenth of the month of Ramadan, and the Holy Qur'an was revealed on the twenty-fourth of the month of Ramadan." Imam Sadiq (pbuh)
"During Laylatul Qadr, the angels, the spirit, and the trusted scribes all descend to the lower heavens and write down whatever Allah decrees that year, and if Allah wishes to advance something or postpone it or add thereto, He orders the angel to erase it and replace it with whatever He decrees." Imam Sadiq (pbuh)
Ibn Abbas is quoted saying, "The Holy Qur'an was revealed as a whole from the Safeguarded Scroll from the heavens to the lower earth on Laylatul Qadr, then Jibrail used to reveal it unto Rasulullah (pbuh) gradually."
Imam Baqir (pbuh), quoting Rasulullah (pbuh) has said that whoever spends Laylatul Qadr adoring his Lord will have all his sins forgiven even if they had numbered as many as the stars in the heavens, the weight of the mountains, or the measures of the seas.
Imam Baqir (pbuh) has said, "The 17th night of the month of Ramadan is when the two parties met, and the 19th is when the lists of the pilgrims is written down, and the 21st is when the successor to the Prophet passed away and Isa (pbuh) was raised to heaven and Musa (pbuh) passed away, whereas the 23rd is hoped to be Laylatul-Qadr."
Ahmed ibn Muhammad ibn Yahya quotes his father saying, "I was in the company of Imam Sadiq (pbuh) when Abu Baseer asked him, 'Which night is the one when one is to plead to his Lord whatever he wishes to plead?' Imam answered him by saying, 'Either the twenty-first or the twenty-third.' He then asked him: 'What if I have no strength to observe both of them?'
Imam said, 'How easy it is to observe them when compared to your pleas!"'
Imam Sadiq (pbuh) has also said: "The twenty-third night of the month of Ramadan is the one when every weighty matter is decided, when trials, tribulations, deaths, and means of sustenance and other matters are determined, and so will whatever Allah decrees to take place for the entire next year; so, congratulations to anyone who remains awake during it bowing, prostrating, contemplating upon his sins, weeping on their account, for if you do all of that, God willing, you Will never be disappointed."
Then he added, "Allah will order an angel to call out during each and every day of the month of Ramadan conveying Allah's message to them thus: ' Good news, O My servants, I have forgiven your past sins and permitted some of you to intercede on behalf of the rest on Lailatul-Qadr except those who break their fast with an intoxicant or those who bear grudge against another Muslim brother!'"
It is narrated that Allah wards off evil and sins and all types of trials on the 25th night from all His servants who fast and grants them light in their hearing and vision; Janna is decorated during Laylatul Qadr's day and night.