What is the interpretation of Allah's saying, the Most High: "Indeed, We sent it down during the Night of Decree"? And how do we fall into sins, and how does one become heedless in recitation and prayer in Ramadan, even with the devils chained up?

The meaning of "Indeed, We sent it down on the the Night of Decree" is that Allah sent down the Qur'an as a complete whole to the lowest heaven on the Night of Decree. It was named as such due to its immense value and virtue, or because in it are decreed what will transpire during the year concerning lifespans, provisions, and destinies.