Tafsir of Al-Isra 17:105

The Revelation of the Qur'an in Stages Allah tells:

وبالحق أنزلناه

And with truth We have sent it down, Allah tells us that His Book, the Glorious Qur'an, has been sent with truth, i.e., it contains the truth, as Allah says:

لكن الله يشهد بما أنزل إليك أنزله بعلمه والمليكة يشهدون

But Allah bears witness to that which He has sent down unto you; He has sent it down with His knowledge, and the angels bear witness. (4:166) meaning, it contains the knowledge which Allah wanted to teach to you, with His rulings, commands and prohibitions.

وبالحق نزل

and with truth it has descended. means, "It has been sent down to you, O Muhammad, preserved and protected, not contaminated or mixed with anything else, with nothing added or taken away. It has come to you with the truth, brought down by one mighty in power, trustworthy and strong, one who is obeyed by the higher group (angels).'

وما أرسلناك

And We have sent you, (O Muhammad),

إﻻ مبشرا ونذيرا

as nothing but a bearer of glad tidings and a warner. a bearer of glad tidings for the believers who obey you and a warner to the disbelievers who disobey you