Here Allah praises Himself for the Noble Qur’an He has revealed to His noble Messenger. This is like the Ayat

{All the praises and thanks be to Allah, Who has sent down to His servant the Book, and has not placed therein any crookedness. (He has made it) straight to give warning of a severe punishment from Him, and to give glad tidings to the believers, who do righteous deeds...} [18:1-2]

Here Allah says:

{Blessed be He.} The verbal form used here implies an ongoing, permanent, eternal blessing.

{Who sent down the criterion } The verb Nazzala is a form which implies something done a great deal and often. This is like the Ayah:

{the Book which He (Nazzala) sent down to His Messenger, and the Scripture which He (Anzala) sent down to those before (him)} (4:136).

Each of the previous Books was sent down at one time, but the Qur’an was revealed gradually, in stages, Ayat after Ayat, rulings after rulings, Surahs after Surahs. This is more eloquent and indicative of greater care for the one to whom it is revealed, as Allah says later in this Surah:

{And those who disbelieve say: "Why is not the Qur'an revealed to him all at once?" Thus, that We may strengthen your heart thereby. And We have revealed it to you gradually, in stages. And no example or similitude do they bring, but We reveal to you the truth, and the better explanation thereof.} (25:32-33)

This Surah was named Al-Furqan, because it is the criterion that decides between truth and falsehood, guidance and misguidance, right and wrong, lawful and unlawful.

{to His servant} This description is one of praise and commendation, because here Allah is connecting him to Himself, describing him as His servant. Allah also described him in this manner when referring to the noblest of events, the Night of the Isra’, as He said:

{Glorified be He Who took His servant for a journey by night} (17:1)

Allah also described him in this way when He described how he stood and called to Him:

{And when the servant of Allah stood up invoking Him in prayer they (the Jinn) just made round him a dense crowd as if sticking one over the other (in order to listen to the Prophet's recitation).} (72:19)

This description is also used here when Allah describes how the Book is revealed to him and how the angel comes down to him:

{that he may be a warner to all nations.} means, he alone has been blessed with this great, detailed, clear Book which,

{Falsehood cannot come to it from before it or behind it, (it is) sent down by the All-Wise, Worthy of all praise (Allah).} (41:42)

The One Who made it the mighty criterion, singled him out to convey it to those who seek the shade of trees and to those who live on the land (i.e., to all of mankind, nomad and settled alike), as the Prophet said:

«I have been sent to the red and the black.»

And he said:

«I have been given five things which no Prophet before me was given.»

Among them he mentioned:

«[Before me] a Prophet was sent only to his own people, but I have been sent to all of mankind.»

And Allah says:

{Say: "O mankind! Verily, I am sent to you all as the Messenger of Allah..."} (7:158),
meaning, the One Who has sent me is the Sovereign of the heaven and the earth, who merely says to a thing “Be!” and it is. He is the one who gives life and causes death. Allah says here:

Allah states that He is above having any offspring or partner. Then He tells us:

meaning, everything apart from Him is created and subject to Him. He is the Creator, Lord, Master and God of all things, and everything is subject to His dominion, control and power.