التفسير التبليغي
(Half of it, or subtract from it a little) (3)
(Half of it, or subtract from it a little) (or add to it) something, meaning the choice is yours regarding standing (in prayer) for half the night or less than that.
(Half of it) (or subtract from it) from the half (a little) to a third.
If we strive during the day but do not strive at night, then it is an incomplete effort, and guidance will not come in its fullness.
The deeds of the night are what give strength to the deeds of the day.
At night, there is solitude with Allah the Almighty, and He opens the hearts of His servants during the day.
Source: التفسير التبليغي