The Necessity to Hold Tightly to the Qur'an (revelation)
So hold fast to what has been revealed to you. Indeed, you are on a straight path.
174.O mankind! Certainly, a proof has come to you from your Lord, and We have sent down to you a manifest light.
175. As for those who have faith in Allah, and hold fast to Him(His revelation), He will admit them to His mercy and grace, and He will guide them on a straight path to Him.
Hold fast, all together, to Allah’s cord(i.e. this Quran), and do not be divided [into sects]. Remember Allah’s blessing upon you when you were enemies, then He brought your hearts together, so you became brothers with His blessing. And you were on the brink of a pit of Fire, whereat He saved you from it. Thus does Allah clarify His signs(proofs, evidences, verses, lessons, revelations, etc.,) for you so that you may be guided.
170. And as to those who hold fast to the Book and perform As-Salat (Iqamat-as-Salat), certainly, We shall never waste the reward of those who do righteous deeds.
171. When We plucked the mountain [and held it] above them as if it were a canopy (and they thought it was about to fall on them): ‘Hold on with power to what We have given you and remember that which is in it, so that you may be Godwary.’
And strive(jihad) hard in Allah's Cause as you ought to strive(jihad). He has chosen you, and has not laid upon you in religion any hardship, it is the religion of your father Ibrahim (Abraham). It is He (Allah) Who has named you Muslims both before and in this (the Quran), that the Messenger may be a witness over you and you be witnesses over mankind! So perform As-Salat (Iqamat-as-Salat), give Zakat and hold fast to Allah(His revelation).He is your Maula (Mawla, Lord, etc.), what an Excellent Maula (Mawla, Lord, etc.) and what an Excellent Helper!
And (O Children of Isra'il, remember) when We took your covenant and We raised above you the Mount (saying): "Hold fast to that which We have given you, and remember that which is therein so that you may acquire Taqwa.
(Taqwa means: Living with constant awareness of Allah’s presence, Striving to protect yourself from anything that distances you from Him, Acting with sincerity, restraint, and humility in your daily choices)
And (remember) when We took your covenant and We raised above you the Mount (saying), "Hold firmly to what We have given you and hear (Our Word). They said, "We have heard and disobeyed." And their hearts absorbed (the worship of) the calf because of their disbelief. Say: "Worst indeed is that which your faith enjoins on you if you are believers."
(It was said to his son): "O Yahya (John)! Hold fast the Scripture [the Taurat (Torah)]." And We gave him wisdom while yet a child. And (made him) sympathetic to men as a mercy (or a grant) from Us, and pure from sins [i.e. Yahya (John)] and he was righteous,