Serīʿ is interpreted in two ways:
1. The phrase serīʿu'l-ḥisāb is used in the sense of 'the One whose reckoning is swift,' as if the time for reckoning has already arrived; as in the following verses:
"And mention the name of Allah upon it and have taqwa (God-consciousness) of Allah. Indeed, Allah is serīʿu'l-ḥisāb {that is, the One whose reckoning is very swift}." (al-Māʾida 5:4)
The verse is as if the reckoning has come and is warning them with it.
"For them is a share of what they have earned. And Allah is serīʿu'l-ḥisāb {that is, the One whose reckoning is very swift}." (al-Baqara 2:202)
It means: "As if the time for reckoning has already come (let them beware)."
"He will find Allah with him, and He will take account of him. Allah is serīʿu'l-ḥisāb {that is, the One whose reckoning is very swift}." (al-Nūr 24:39)
It means: "As if the time for reckoning has already come (let them beware)."
There are many similar statements.
2. The phrase serīʿu'l-ḥisāb means 'the One who, when He calls the created beings to account, completes their reckoning swiftly'; as in the following verse:
"On that Day every soul will be recompensed for what it earned. No injustice today! Indeed, Allah is serīʿu'l-ḥisāb {that is, the One who, when He begins the reckoning, will swiftly complete the accounts}." (al-Muʾmin 40:17)
Muqātil b. Sulaymān said: It is narrated from Ibn ʿAbbās that he said: "Allah will complete the reckoning of the created beings in a period as brief as the duration between two mornings in the days of this world. The statement of Allah, 'That Day, the companions of Paradise will have the best settlement and the fairest resting place' (al-Furqān 25:24), refers to this."
The companions of Paradise will be in Paradise, and the companions of Hell will be occupied within the walls. And the statement, "And He is asraʿu'l-ḥāsibīn [the swiftest of those who take account]" (al-Anʿām 6:62), is also of this kind.