All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
There are many Hadeeths narrated on the virtue of reading Surat Al-Kahf on Friday. For instance, it was narrated on the authority of Abu Sa‘eed Al-Khudri that the Prophet, sallallaahu ‘alayhi wa sallam, said: “Whoever reads Surat Al-Kahf on Friday will have a light that will shine for him in the interval between that Friday and the next.” [Al-Bayhaqi and Al-Haakim, Al-Albaani: Saheeh]
It was narrated on the authority of Abu Sa‘eed Al-Khudri that the Prophet, sallallaahu ‘alayhi wa sallam, said: “Whoever reads Surat Al-Kahf on Friday will have a light that will shine for him between him and the Ancient House.” [Al-Bayhaqi and Al-Haakim, Al-Albaani: Saheeh]
It was narrated on the authority of Ibn ‘Umar that the Prophet, sallallaahu ‘alayhi wa sallam, said: “Whoever reads Surat Al-Kahf on Friday, a light will shine for him from under his feet up to the heavens that will light up for him on the Day of Resurrection, and he will be forgiven (for the sins he committed) between that Friday and the next.” [Al-Munthiri in At-Targheeb wat-Tarheeb and said that Abu Bakr ibn Mardawayh narrated it in his Tafseer through a good chain of narrators]
The light mentioned in these texts may be intangible light, which means that if the Muslim reads Surat Al-Kahf on Friday, this will prevent him from committing sins and guide him to the right path from that Friday until the next, just like light helps us to see things.
The light may also be tangible, which means that a light will shine for him from under his feet and appear on his face on the Day of Resurrection, as well as having brightness and splendor on his face in this worldly life. The second interpretation is more plausible because it is consistent with the Hadeeth of Ibn ‘Umar .
Note: The virtue cited in the above-mentioned texts is also granted to the Muslim who reads Surat Al-Kahf on Thursday night. Al-Munaawi said, "It is recommended to read Surat Al-Kahf on Friday and the night before as stated by Ash-Shaafi‘i ." He adds that Al-Haafith Ibn Hajar said, "This is mentioned in the narrations about Friday and the narrations about Thursday night. This can be reconciled by saying that what is meant is the day including its night and the night including its day."
Allaah Knows best.