Is a person who experiences severe and distressing blasphemous whispers concerning the essence of God and creed considered sinful and blameworthy, and will they be among the people of Hellfire or the people of Paradise, especially given their love for God, His Messenger, and their religion, their efforts in striving and inviting to Islam, and their knowledge that these whispers are from Satan?

As long as you love inviting to Allah, sit with the righteous, and frequently supplicate and recite the Quran, then you are upon good. What you find of whispers (waswas) is from the devil's plot against you, and it can be considered a sign of goodness. Muslim narrated from Abu Hurayrah that the Prophet (peace and blessings be upon him) said regarding waswas: "That is clear faith." Imam Ahmad and Abu Dawud narrated from Ibn Abbas that the Prophet (peace and blessings be upon him) said concerning similar matters: "Praise be to Allah who confined his (the devil's) plot to whispers." Ignoring these whispers and not paying attention to them is the greatest means of treatment. Continue to supplicate, be diligent in acts of obedience, keep company with the righteous, and frequently repent and seek forgiveness, in addition to performing Ruqyah (definition) Shar'iyyah. We advise you to avoid excessive searching and reading of fatwas and articles that speak about waswas, because preoccupation with them may increase them.