For a person to succeed in seeking knowledge it’s not just about learning and acting upon it, rather the ilm must be kept in a safe vessel and this vessel is the heart.
If a person has been doing haram for years, whether it be watching haram movies, watching filth online, girlfriends, even too much of something like video games, this occupies their heart and causes ones heart to become hardened and full of darkness. For the persons ilm to benefit them, the heart needs to be cleaned and this process takes a long time. The longer the person was in jaahiliyyah, the more their heart will need cleansing.
This is something we definitely need to work on.
إِلَّا مَنْ أَتَى اللَّهَ بِقَلْبٍ سَلِيمٍ
Allah mentions the clean sound heart here and we know this can’t be one that is filled with love of football players or game characters etc rather it’s full of love of Allah and a desire to please Him and wanting to be with Him, like an urge, a longing and only then is the person ready for seeking serious knowledge.
And as Uthman (ra) said, a person’s secrets always come out, whether it’s something good or bad and it’ll be shown on his face or through a slip of the tongue .
That’s why the way a person speaks reflects what’s inside their hearts so if he/she always talk about money or talking about others or about irrelevant things then this shows what is inside their heart. Similarly if one is always talking about Allah and His Messenger (saw), this shows what’s inside their hearts too.