At the beginning of Surah Qalam, Allah reminds the tribe of the Prophet, Quraysh, that he had the best character. Allah was reminding them that they knew who he was, and they knew he would not lie, so they should therefore think about and accept his message and trust him, just like they had trusted him for decades prior.
"And you are truly ˹a man˺ of outstanding character." (The Clear Quran; Qalam, 4)
