What does the Prophet ﷺ mean by his saying: If you knew what I know.

You would laugh little and weep much.

Yes, the matters that the Prophet knows.

ﷺ about the conditions of the Day of Judgment, what happens there, and the Fire.

And the punishment it contains. If a person truly knew this.

He would not laugh, and fear would lead him to weep.

And little laughter, because the matter is not easy. We have been created in this world to worship Allah, the Blessed and Exalted. A person reflects.

On what he might face in his grave, on what he might face in his Hereafter. This pushes him to work hard, to strive, and not to waste time in laughter and other things.

This is the meaning of the Prophet's ﷺ hadith, and Allah knows best.