Nasai

Two different meanings are intended by the punishment of the grave:

➊ The questioning and answering in the grave, which is also called the trial (fitnah) of the grave.

➋ The torments that reach a person in the grave due to sins. In some hadiths, the first meaning is intended, and in others, the second. In the above-mentioned verse, the questioning and answering of the grave is meant. Similarly, when the negation of the punishment of the grave is mentioned regarding martyrs, those who die of plague, cholera, or accidental death, what is meant is the negation of questioning and answering. Whereas in the narration of Sa'd radi Allahu anhu, the second meaning is intended, and this (i.e., the squeezing of the grave) happens to everyone—to the extent of being squeezed—except for the Prophets (alayhim as-salam). Beyond this, the punishment is according to each person's sins, to the extent that for some it will continue until the Day of Resurrection.

Benefits and Issues:

➊
By “firm word” is meant the kalimah of tawhid (the declaration of the oneness of Allah).
A believer, by Allah’s tawfiq (divine enablement), remains steadfast upon this in worldly life, as a result of which he remains firm during the questioning in the grave.
A hypocrite, on the other hand, does not remain steadfast upon this in worldly life; rather, his faith is unstable,
and he remains entangled in doubts and suspicions.
Therefore, even in this first stage of the Hereafter (the grave),
he is unable to give the correct answer.

➋
Punishment in the grave can occur not only for the sin of doctrinal hypocrisy (nifaq i‘tiqadi), but also for lesser sins.
For example, not taking care to protect one’s body and clothes from urine, or causing discord between people by conveying statements from one to another, etc.