﴿ وَلَقَدِ ٱسْتُهْزِئَ بِرُسُلٍۢ مِّن قَبْلِكَ فَأَمْلَيْتُ لِلَّذِينَ كَفَرُوا۟ ثُمَّ أَخَذْتُهُمْ ۖ فَكَيْفَ كَانَ عِقَابِ ﴾

“And, indeed, [even] before thy time have [God's] apostles been derided, and for a while I gave rein to those who were [thus] bent on denying the truth: but then I took them to task - and how awesome was My retribution!”

it was said to comfort him: وَلَقَدِ اسْتُهْزِئَ بِرُ‌سُلٍ مِّن قَبْلِكَ فَأَمْلَيْتُ لِلَّذِينَ كَفَرُ‌وا ثُمَّ أَخَذْتُهُمْ ۖ فَكَيْفَ كَانَ عِقَابِ (And Messengers have been mocked at before you, so I let the disbelievers go on for a while. Then I seized them. So, how was My punishment?) In other words, it means that conditions faced by the Holy Prophet were not faced by him alone. There were prophets before him who had been facing similar conditions when their deniers were not seized immediately upon the commitment of their crime and they continued to make fun of the prophets. When they reached the limit, they were seized by Divine punishment and what a seizure that was which left none of them active enough to go on with their confrontation.