﴿ وَقَالَ رَجُلٌۭ مُّؤْمِنٌۭ مِّنْ ءَالِ فِرْعَوْنَ يَكْتُمُ إِيمَٰنَهُۥٓ أَتَقْتُلُونَ رَجُلًا أَن يَقُولَ رَبِّىَ ٱللَّهُ وَقَدْ جَآءَكُم بِٱلْبَيِّنَٰتِ مِن رَّبِّكُمْ ۖ وَإِن يَكُ كَٰذِبًۭا فَعَلَيْهِ كَذِبُهُۥ ۖ وَإِن يَكُ صَادِقًۭا يُصِبْكُم بَعْضُ ٱلَّذِى يَعِدُكُمْ ۖ إِنَّ ٱللَّهَ لَا يَهْدِى مَنْ هُوَ مُسْرِفٌۭ كَذَّابٌۭ ﴾

“At that, a believing man of Pharaoh’s family, who [until then] had concealed his faith, exclaimed: “Would you slay a man because he says, ‘God is my Sustainer’ - seeing, withal, that he has brought you all evidence of this truth from your Sustainer? Now if he be a liar, his lie will fall back on him; but if he is a man of truth, something [of the punishment] whereof he warns you is bound to befall you: for, verily, God would not grace with His guidance one who has wasted his own self by lying [about Him].”

In verse 28, it was said: يَكْتُمُ إِيمَانَهُ (who had kept his faith secret). This tells us that a person who does not declare his 'iman (faith) before people, yet remains staunch in his faith by heart, then, this person is a believer. But, it stands proved from clear textual authority (of the Qur'an and Hadith) that, for 'iman to be acceptable, the simple certitude of the heart is not enough, instead, it is subject to the condition of a verbal confession and declaration. Unless the person concerned declares it verbally, he or she will not be regarded as a believer. However, making this verbal declaration before people publicly is not necessary. The only reason why it is needed is that unless people come to know about the person's 'iman, they would remain unable to interact with him or her in the same way as they do with Muslims. (Qurtubi) Earlier in the verse, by saying: مُّؤْمِنٌ مِّنْ آلِ فِرْ‌عَوْنَ (a believing man from the House of the Pharaoh), it is virtually demonstrated that the believer, in his ensuing dialogue with Pharaoh and his people, invited them toward truth and faith as well as restrained them from killing Sayyidna Musa (علیہ السلام) .