Abbas - Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
(Lo! those who distort Our revelations) those who deny Our signs-Muhammad (pbuh) and the Qur'an-(are not hid from Us) none of their works is hidden from Us. (Is he who is hurled into the Fire) Abu Jahl and his host (better, or he who cometh secure) from the torment (on the Day of Resurrection) this refers to Muhammad (pbuh) and his Companions? (Do what ye will) O people of Mecca; this is a threat made to them. (Lo! He is Seer of what ye do) He will requite your works.
Indeed those who blaspheme (yulhidūna derives from [the verb] alhada, or lahada, ‘he blasphemed’) Our signs — the Qur’ān, by denying [its truth] — are not hidden from Us, and We will requite them. Is one who is cast into the Fire better [off], or one who arrives secure on the Day of Resurrection? Act as you wish; indeed He is Seer of what you do — this is [meant as] a threat for them.
(Falsehood cannot come to it from before it or behind it,) means, there is no way to corrupt it, because it has been sent down by the Lord of the worlds. Allah says:
تَنزِيلٌ مِّنْ حَكِيمٍ حَمِيدٍ
((it is) sent down by the All-Wise, Worthy of all praise.) meaning, He is Wise in all that He says and does, Praiseworthy in all that He commands and forbids; everything that He does is for praiseworthy purposes and its consequences will be good.
(Nothing is said to you except what was said to the Messengers before you.) Qatadah, As-Suddi and others said, "Nothing is said to you by way of rejection and disbelief, that was not said to the Messengers who came before you. Just as you have been rejected, they were also rejected. Just as they bore their people's insults with patience, so too you must bear your people's insults with patience.''
وَإِنَّ رَبَّكَ لَذُو مَغْفِرَةٍ
(Verily, your Lord is the Possessor of forgiveness,) means, for those who turn to Him in repentance.
وَذُو عِقَابٍ أَلِيمٍ
(and (also) the Possessor of painful punishment.) means, for those who persist in disbelief, transgression and stubborn opposition.
Maududi - Sayyid Abul Ala Maududi - Tafhim al-Qur'an
After telling the common people in a few sentences that the doctrine of Tauhid and the Hereafter to which Muhammad (upon whom be Allah's peace) is inviting them, is rational and the signs of the universe testify to its being right and true, the discourse again tunes to the opponents who were determined to oppose it stubbornly.
The word yulhidun in the original is derived from ilhad which means to deviate, to turn away from the right to the wrong path, to adopt crookedness. Thus, ilhad in the Revelations of Allah would mean that instead of understanding them in their clear and straightforward meaning one should misconstrue them and go astray and also lead others astray. One of the devices being adopted by the disbelievers of Makkah to defeat the message of the Qur'an was that they would hear the verses of the Qur'an and then would isolate one verse from its context, tamper with another, misconstrue a word or a sentence and thus raise every sort of objection and would mislead the people, saying that the Prophet had said such and such a thing that day.
These words imply a severe threat. The All-Powerful Ruler's saying that the acts of such and such a person are not hidden from Him by itself contains the meaning that he cannot escape their consequences.
"A mighty Book": An unchanging Book, which cannot be defeated by tricks and cunning devices, which the worshipers of falsehood are employing against it. It has the force of the Truth in it, the force of true knowledge, the force of argument and reason, the force of eloquence and style, the force of Divinity of God Who sent it, and the force of the personality of the Messenger who presented it. No one, therefore, can defeat it by falsehood and hollow propaganda.
"Falsehood.... from before it" means that none can succeed in proving anything wrong or any teaching false in the Qur'an by making a frontal attack on it;.... nor from behind it" means that nothing can be discovered till Resurrection which may be opposed to the truths and realities presented by the Qur'an; no new science, if it is really a "science", can be propounded, which may contradict the knowledge contained in the Qur'an; no new experiment or observation can be made to prove that the guidance given to man by the Qur'an in respect of the beliefs, morality, law, civilization or culture, and economic, social and political lift is wrong. That which this Book has declared as the Truth can never be proved to be falsehood and that which it has declared as falsehood can never be proved to be the truth. Furthermore, it also means that whether falsehood makes a frontal attack, or makes a surprise attack by deception, it cannot defeat the message which the Qur'an has brought. In spite of all sorts of open and secret machinations of the opponents the message will spread and none shall be able to defeat and frustrate it.