﴿ وَقَالُوا۟ لَوْلَآ أُنزِلَ عَلَيْهِ مَلَكٌۭ ۖ وَلَوْ أَنزَلْنَا مَلَكًۭا لَّقُضِىَ ٱلْأَمْرُ ثُمَّ لَا يُنظَرُونَ ﴾

“They are saying, too, "Why has not an angel (visibly] been sent down unto him?" But had we sent down an angel, all would indeed have been decided, and they would have been allowed no further respite [for repentance.”

Please check ayah 6:11 for complete tafsir.