He asks: what is the wisdom behind the obligation of ghusl?

For those who practice self-gratification—may Allah protect us and you from it. O Allah, grant everyone well-being.

The Prophet ﷺ said: Water is from water.

Water is from water, meaning the water of ghusl is because of the water of seminal fluid.

Water from water means the water of ghusl is due to seminal fluid; as long as seminal fluid is released, ghusl becomes obligatory for a person, whether through intercourse

or without intercourse, and even intercourse without ejaculation also makes it obligatory.

Ghusl is required, and Allah knows best. The time has entered.