Kutub (books) is plural for Kitab (a book). They are called Kutub because they are written (maktoob). Books, here means the Books that Allah sent down to His Messengers as a mercy and guidance for mankind, to lead them to what brings them happiness in this life and in the Hereafter.
There are four aspects of believing in the Books
1. To believe that they are truly sent down by Allah.
2. To believe in the Books that mankind were informed of, like the Qur’an, sent down to Muhammad (sallallaahu alaihi wa-sallam), the Torah, sent down to Moses, the Injeel (the Gospel), sent down to Jesus and the Zaboor (the Psalms), sent down to David. We also believe in the other Books, sent down by Allah, even though we do not know their names.
3. To believe in whatever the Books contained, like whatever is contained in the Qur’an and sections of previous Books that have not been corrupted.
4. To implement the Commandments contained in these Books, unless Allah commanded to the contrary through Naskh (over ruling). We must accept whatever these Books contained of Commandments, even if we do not know the wisdom behind them. All previous Books were over-ruled by the Qur’an. Allah said, what translated means, “And We have sent down to you (O Muhammad sala Allah ‘alihi wasallam) the Book (this Quran) in truth, confirming the Scripture that came before it and Mohayminan (trustworthy in highness and a witness) over it (old Scriptures).” [Al-Ma’idah 5:48].
Transliteration: Waanzalna ilayka alkitaba bialhaqqi musaddiqan lima bayna yadayhi mina alkitabi wamuhayminan AAalayhi
This means that the Qur’an is dominant over all other Books. Therefore, no Commandment contained in other than the Qur’an can be implemented unless it is in agreement with the Qur’an.
Benefits Of Believing In The Books
1. Knowing that Allah takes care of His slaves by sending down Books for their guidance.
2. Knowing Allah’s Wisdom in whatever He commands. He commanded each nation with what is suitable for them, “To each among you, We have prescribed a Law and a Clear Way.” [Al-Ma’idah 5:48].
Transliteration: likullin jaAAalna minkum shirAAatan waminhajan
3. Thanking Allah for His bounties, because He sent down these Books to lead mankind to guidance.