What is the reason a person does not remember what he sees in a dream, and is there a way to remember it?

It is natural for a person not to remember what happens in their sleep. What is required is to focus one's energy while awake on learning the Quran, the Sunnah (definition), and the sciences of Islamic law. By doing so, one will attain good, for the Prophet, peace and blessings be upon him, said: "The best among you is he who learns the Quran and teaches it," and he also said: "Whomever Allah wishes good for, He grants him understanding in the religion."