وَيَسْتَجِيبُ ٱلَّذِينَ ءَامَنُوا وَعَمِلُوا ٱلصَّـٰلِحَـٰتِ وَيَزِيدُهُم مِّن فَضْلِهِ ۚ وَٱلْكَـٰفِرُونَ لَهُمْ عَذَابٌ شَدِيدٌ

According to the law governing this world, Truth appears here in the form of Truth and falsehood in the form of falsehood. A false soul cannot beget Truth. For this reason it is not possible for a non-prophet to use prophetic language. If an individual is not a prophet, but by telling lies, claims to be so, then the style of the false prophet will necessarily creep into his utterances. No ordinary person can speak in the style of a true prophet. ‘If God so willed, He can seal your heart’ means, ‘Had you made false allegations against God, your heart would have been sealed by the will of God.’ Under these circumstances, by the divine laws of nature, you would have found it impossible to deliver the pure, divine discourse, the signs of which are clearly seen in your utterances. The fact is that the sublime words of the Prophet themselves prove him to be a prophet of God. Had he not really been the prophet of God, such utterances would not have fallen from his lips. Those who oppose the Truth do so, not at the dictates of their heart or conscience, but simply out of obstinacy and hostility. Such people are, so to say, held guilty in the court of their own conscience. God’s judgement of them is final, except when they repent and seek God’s pardon.

— Source: Tazkirul Quran (Maulana Wahiduddin Khan) via Quran.com (42:26)