And they swore by Allah their strongest oaths that if a warner (35:42)

﴿وَأَقْسَمُوا بِاللَّهِ جَهْدَ أَيْمَانِهِمْ لَئِن جَاءَهُمْ نَذِيرٌ لَّيَكُونُنَّ أَهْدَىٰ مِنْ إِحْدَى الْأُمَمِ ۖ فَلَمَّا جَاءَهُمْ نَذِيرٌ مَّا زَادَهُمْ إِلَّا نُفُورًا﴾
[ فاطر: 42]

35:42 And they swore by Allah their strongest oaths that if a warner came to them, they would be more guided than [any] one of the [previous] nations. But when a warner came to them, it did not increase them except in aversion.

These denying disbelievers swore a solemn and affirmed oath that if a messenger from Allah came to them to warn them of His punishment, they would be more guided and follow the truth more than the Jews, Christians and others.
Yet when Muhammad ( peace be upon him ) came to them after being sent by His Lord, and he warned them of Allah’s punishment, his coming only increased them in aversion to the truth and adherence to falsehood.
They did not fulfil the solemn oaths that they took that they will be more guided than those who preceded them.

And they swore by Allah their most binding oath, that if a warner came to them, they would be more guided than any of the nations (before them), yet when a warner (Muhammad SAW) came to them, it increased in them nothing but flight (from the truth),

phonetic Transliteration

Waaqsamoo biAllahi jahda aymanihim lain jaahum natheerun layakoonunna ahda min ihda alomami falamma jaahum natheerun ma zadahum illa nufooran

Abdullah Yusuf Ali - Translation

They swore their strongest oaths by Allah that if a warner came to them, they would follow his guidance better than any (other) of the Peoples: But when a warner came to them, it has only increased their flight (from righteousness),-

Safi-ur-Rahman al-Mubarakpuri

And they swore by Allah their most binding oath that if a warner came to them, they would be more guided than any of the nations; yet when a warner came to them, it increased in them nothing but flight (from the truth).

Page 439 English transliteration