A summary of the concepts held by the Ahl al-Sunnah.
A sound heart does not imply naivety or heedlessness.
A sound heart does not mean being ignorant of evil and its proponents.
Nor does it mean being easily deceived by them.
Rather, the possessor of a sound heart
recognizes evil and avoids it.
He knows the people of evil and is not deceived by them.
Just as it was narrated from the Commander of the Faithful, ‘Umar ibn al-Khattab, may Allah be pleased with him,
that he said:
"I am not a deceiver, nor does a deceiver deceive me."
The "deceiver" (al-khabb) is the base and treacherous person.
Thus, ‘Umar, may Allah be pleased with him, was too intelligent to be deceived,
and too pious to deceive others.
The difference between a sound heart and naivety or heedlessness
is that a sound heart is characterized by
not desiring evil after having recognized it,
remaining safe from it despite knowing and understanding it.
As for naivety and heedlessness,
they are forms of ignorance and lack of awareness.
This is not praiseworthy; rather, it is a deficiency.
True perfection is for the heart to be knowledgeable of evil while remaining free from the desire to commit it.