Allah tells us that He does not guide those who turn away from remembering Him and who are heedless of that which He revealed to His Messenger ﷺ, those who have no intention of believing in that which he has brought from Allah. This kind of people will never be guided to faith by the signs of Allah and the Message which He sent His Messengers in this world, and they will suffer a painful and severe punishment in the Hereafter. Then Allah informs us that His Messenger ﷺ is not a forger nor a liar, because the one who fabricates falsehood about Allah and His Messenger ﷺ is the most evil of creatures.

(Verily, those who do not believe in Allah's Ayat,) Allah will not guide them, and theirs will be a painful punishment, meaning, the disbelievers and heretics who are known to the people as liars. The Messenger Muhammad ﷺ, on the other hand, was the most honest and righteous of people, the most perfect in knowledge, deeds, faith and conviction. He was known among his people for his truthfulness and no one among them had any doubts about that - to such an extent that they always addressed him as Al-Amin (the Trustworthy) Muhammad. Thus when Heraclius, the king of the Romans, asked Abu Sufyan about the attributes of the Messenger of Allah ﷺ, one of the things he said to him was, "Did you ever accuse him of lying before he made his claim?" Abu Sufyan said, "No". Heraclius said, "He would refrain from lying about people and then go and fabricate lies about Allah?"