Should we consider the hearts of non-believers to be sealed?
We don’t have the right to consider anybody's heart to be sealed, whether they are Muslims or non-Muslims.
If a disbeliever has not received the message of Islam properly, then he has the chance to return to guidance when the message reaches him. The heart becomes sealed when a person who believes later turns to disbelief.
As described in the verse of the Qur’an, the translation of which is:
“That is because they believed, and then disbelieved; therefore their hearts are sealed, so they understand not.” 
This is the turning away from the Truth in the ultimate sense.
 Al-Quran Surah al Munafiqoon- 63: 3< Back to Questions