The punishment for those who do not practice their knowledge

The punishment for those who don't practice their knowledge:

Those who do not act upon their knowledge will be punished in the hereafter.

The Prophet (S) said, “On the night that I was ascended up to the heavens (Al-Miraaj), I came upon a people whose lips were being cut off by scissors made from Fire. Every time their lips were severed, they would be brought back and formed again. So I said: ‘O Jibreel, who are these people?’ He said: ‘They are speakers from your nation, who say words but do not do deeds, and who read the Book of Allah yet do not act (on it).”‘
[Al Bayhaqi, classed as Hasan]

In another hadith the Prophet (S) said, “A man will be brought on the Day of Judgment and thrown into the Hell-fire where his intestines will spill out. So it will be said (to him): ‘Weren’t you the one who used to command good and forbid evil?’ So he will say: “I used to command you to do good yet not do it myself. And I used to forbid you from evil yet commit it myself.”‘
[Bukhari and Muslim]

Gain Beneficial Knowledge:

The Prophet (S) used to make duaa for beneficial knowledge:

اللَّهُمَّ انْفَعْنِي بِمَا عَلَّمْتَنِي وَ عَلِّمْنِي مَا يَنْفَعُنِي وَ زِدْنِي عِلْمًا

Allahumma-infa’nī bimā ‘alamtanī wa ‘allimnī mā yanfa’unī wa zidnī ‘ilmā

O Allah, benefit me from that which You taught me, and teach me that which will benefit me, and increase me in knowledge.
(Reported in Sunan ibn Maajah)

If knowledge does not make you a better Muslim, through your character and worship, then it is not benefiting to you.

Seeking Knowledge is Obligatory:

The Prophet (S) said: “Seeking knowledge is an obligation upon every Muslim.” [Sunan Ibn Mâjah]

It is obligtory for one to seek knowledge about the matters that make his belief (`aqeedah), worship and actions correct. It is not permissible to neglect this kind of knowledge or to be distracted from seeking it, as without this knowledge one may engage in prohibited actions.

Knowledge is action:

Allah’s Messenger (S) said, “The two feet of the servant will not move (from standing before Allah) on the Day of Judgment until he is asked about four things: on his life and how he spent it; on his knowledge and what he did with it; on his wealth and where he earned it and how he spent it; and on his body and in what way he utilized it.”
[Saheeh, reported by At-Tirmidhi]

Each of us will be questioned about our knowledge and how we used it.

Seek Islamic Knowledge with the Right Intention:

Seeking knowledge of the deen for wordly purposes (i.e., a wrong intention) will prevent one from even smelling the fragrance of Jannah.

The Prophet (S) said, “Whoever acquires knowledge not learning it except to achieve some worldly gain will not perceive the fragrance of Paradise on the Day of Judgment.”
[Ahmad, Saheeh]