Abbas - Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
(Then, even after that, you turned away) you turned your back on the covenant, (and if it had not been for the grace of Allah upon you) by deferring His punishment (and His mercy) by sending Muhammad (pbuh) to you (you had been among the losers) you would have among the duped who are exposed to Allah's punishment.
Then you turned away, you refrained, thereafter, by turning towards the lower aspect, and but for God's bounty, in guiding the intellect, and His mercy towards you, through the light of insight and [the light of] the Law, you would have been among the losers.
Allah reminded the Children of Israel of the pledges, covenants and promises that He took from them to believe in Him alone, without a partner, and follow His Messengers. Allah stated that when He took their pledge from them, He raised the mountain above their heads, so that they affirm the pledge that they gave Allah and abide by it with sincerity and seriousness. Hence, Allah's statement,
(And (remember) when We raised the mountain over them as if it had been a canopy, and they thought that it was going to fall on them. (We said): "Hold firmly to what We have given you (Tawrah), and remember that which is therein (act on its commandments), so that you may fear Allah and obey Him.'') (7:171).
The mount mentioned here is At-Tur, just as it was explained in Surat Al-A`raf, according to the Tafsir of Ibn `Abbas, Mujahid, `Ata', `Ikrimah, Al-Hasan, Ad-Dahhak, Ar-Rabi` bin Anas and others. This is more obvious. There is another report from Ibn `Abbas saying; `The Tur is a type of mountain that vegetation grows on, if no vegetation grows on it, it is not called Tur.' And in the Hadith about the trials, Ibn `Abbas said; "When they (the Jews) refused to obey, Allah raised the mountain above their heads so that they would listen.''
Al-Hasan said that Allah's statement,
خُذُواْ مَآ ءَاتَيْنَـكُم بِقُوَّةٍ
(Hold fast to that which We have given you) means, the Tawrah. Mujahid said that the Ayah commanded, "Strictly adhere to it.'' Abu Al-`Aliyah and Ar-Rabi` said that,
وَاذْكُرُواْ مَا فِيهِ
(and remember that which is therein) means, "Read the Tawrah and implement it.'' Allah's statement,
(Then after that you turned away. Had it not been for the grace of Allah) means, "Yet, after the firm pledge that you gave, you still deviated and broke your pledge'';
فَلَوْلاَ فَضْلُ اللَّهِ عَلَيْكُمْ وَرَحْمَتُهُ
(Had it not been for the grace and mercy of Allah upon you), meaning, by forgiving you and by sending the Prophets and Messengers to you,
لَكُنتُم مِّنَ الْخَـسِرِينَ
(Indeed you would have been among the losers) meaning, in this life and the Hereafter due to their breach of the covenant.
Maududi - Sayyid Abul Ala Maududi - Tafhim al-Qur'an
The way this incident has been described at different places in the Qur'an, shows that it was at that time a well known incident among the Israelites, but now it is difficult to understand and know what actually happened. One may, however, understand that at the time of making the covenant at the foot of the mountain a dreadful situation was created and it so appeared that the mountain was going to fall upon them. A similar scene has been depicted in Surah AI-A'raf, VII: 171. (Please see E.N. 132 of VII, Al-A'raf) Although its description in the Bible is a little different from that of the Talmud, it depicts the scene very vividly: "And mount Sinai was altogether on a smoke, because the Lord descended upon it in fire: and the smoke thereof ascended as the smoke of a furnace, and the whole mount quaked greatly." (Exodus, 19: 18.) "And all the people saw the thunderings, and the lightnings, and the noise of the trumpet, and the mountain smoking : and when the people saw it, they removed, and stood afar off. And they said unto Moses, Speak thou with us, and we will hear : but let not God speak with us, lest we die." (Exodus, 20 :1819).
And when We made a covenant for you and We raised above you the mount “Take forcefully what We have given you and remember what is in it so that you might preserve yourselves.” Then you turned away thereafter and but for God's bounty and His mercy toward you you would have been among the losers. He سبحانه made a covenant with all responsible beings and some responded willingly because He made Himself known to them and they declared His unity fa-waḥḥadūhu. Other people responded unwillingly because He veiled them so they did not want to recognize Him fa-jaḥadūhu. There is no proof more powerful than the eyewitnessing of the mount Ṭūr He raised above them which was a mountain jabal but they lacked the light of inner sight baṣīra and so the witnessing of physical vision baṣar did not benefit them. Then you turned away thereafter that is you returned to disobedience after witnessing the signs with your own eyes. If not for His decree in granting respite and His forbearance through acts of grace He would punish you without delay and cause a great misfortune to descend upon you and your deeds would be entirely a loss.