In The Name of Allaah, The Most Merciful, The Bestower of Mercy

Shaikh Uthaymeen [rahimahullaah] said:
If a person does not act on the knowledge [he has acquired], it will come to nothing. He will be deprived of blessing [in that knowledge] and will forget it, because Allaah [The Most High] said:

So because of their breach of their covenant, We cursed them, and made their hearts grow hard. They change the words from their (right) places and have abandoned a good part of the Message that was sent to them.
[Surah Al-Maa’idah’ Aayah 13]

This forgetfulness includes both the [removal of knowledge] from one’s memory as well as not acting upon it. But as for when a person acts upon the knowledge [he has acquired], then indeed Allaah [The Most High] increases him in guidance and piety, just as Allaah [The Most High] said:

As for those who accept guidance, He increases their guidance, and bestows on them their piety.
[Surah Muhammad’ Aayah 17]