The Seder night is called 'Leil Shimurim', as it is stated (Exodus 12:42): "It is a night of vigil for the Lord to bring them out from the land of Egypt; this same night is a vigil to the Lord for all the children of Israel throughout their generations."

One must ponder why the phrase 'Leil Shimurim' is repeated – the first time: 'It is a night of vigil for the Lord', and again: 'this same night is a vigil to the Lord for all the children of Israel throughout their generations.' Indeed, all the commentators have addressed this, and we will present their words and explain them. However, before we do so, we will preface with a short introduction:

The concept of 'shmira' (guarding) has four different meanings:

The first and simplest meaning is guarding from harm, distress, and the like.

The second meaning is waiting and anticipation, as is said concerning Joseph and his dreams (Genesis 37:11): "and his father kept the matter in mind," and Rashi explains, "kept the matter – he was waiting and anticipating when it would come," and similarly: "keeping faith" (Isaiah 26:2), and "You do not keep track of my sin" (Job 14:16), meaning, You do not wait, end quote.

The third meaning is caution regarding something, to do or not to do it, as it is said (Deuteronomy 5:12): "Keep the Shabbos day to sanctify it." That is, be cautious on the Shabbos day to refrain from work. Similarly: "so that you may fear the Lord your God, to keep all His statutes and commandments which I command you" (ibid. 6:2), meaning to be cautious in all His statutes and commandments to do them. There are many other examples like these. All of them imply caution in doing or not doing something.

The fourth meaning is the reservation of something for a specific purpose. As is commonly said in colloquial language: 'I am keeping this place for someone,' or: 'I am keeping this item for a certain purpose,' meaning to reserve, allocate, designate, or earmark – Reserve in English. Presumably, this is also the root of the term 'mishmar', common in the yeshiva world, meaning diligent study deep into the night until the time of Shacharit the next morning – that this night is reserved, designated, and dedicated to Torah study.