And this is the language of the Ramban on the matter: "And the reason for 'It is a night of watching unto the Lord for all the children of Israel throughout their generations' – this night that was kept by Hashem to bring them out of Egypt, is unto the Lord, meaning, sanctified to His name, a night of watching for all the children of Israel throughout their generations, that they should keep it to serve Him by eating the Pesach and remembering the miracles, and to give praise and thanks to His name, as it is said (Exodus 13:10): 'You shall therefore keep this ordinance,' and it is said (Deuteronomy 16:1): 'Observe the month of Aviv,' end quote."

I have greatly toiled over understanding his words, and there were several perspectives I had on this, but Baruch Hashem, I finally reached a conclusion. It seems that the words of the Ramban consist of three parts, and we shall see this within his language: [1] That this night was kept by Hashem to bring them out of Egypt. [2] It is unto the Lord, meaning, sanctified to His name. [3] A night of watching for all the children of Israel throughout their generations, that they should keep it to serve Him, etc.

And the explanation of the matter: the intention of the verse in its initial words, 'It is a night of watching unto the Lord to bring them out of the land of Egypt' – this night was kept by Hashem to bring them out of Egypt, and in this, the Ramban follows the path of Rashi, that the usage of the word 'watching' the first time is in the sense of waiting and anticipation, that this night was for Hashem a night of waiting and anticipation to bring them out of Egypt. This is the first part of the Ramban's words.

Furthermore, he deduced from the word 'it is' – it would have sufficed to write 'a night of watching unto the Lord,' and it is written 'a night of watching it is unto the Lord' – that this night 'it is unto the Lord,' meaning, sanctified to His name. In this, the word 'watching' serves in the sense of designation and dedication, that this night is designated and dedicated throughout generations to the Lord, that Hashem is, as it were, the 'Guest of honor' on this night. This is the second part of the Ramban's words.

The Ramban continues and explains, what is the practical expression of this designation and dedication? How do we, as it were, host the Guest of honor on this night? – the Ramban explains that the answer to this comes in the words: "a night of watching for all the children of Israel throughout their generations," that by keeping and fulfilling the obligations of this night, by observing it to serve Him through eating the Pesach and remembering the miracles, and giving praise and thanks to His name – in this, the purpose of this night is fulfilled, which was designated and dedicated to the Lord. In this, the word 'watching' serves in the sense of careful observance and fulfillment. This is the third part of the Ramban's words.