He makes clear,
Paradise was made for tender hearts; hell, for loveless hearts.
On these words and in similar comments, Voltaire draws a distinction of the good (tender) heart, one that produces (and receives) love.
As the reasons or causes for the good heart however, the Bible (perhaps Christianity) is dismissed, no application is his view based on:
The Bible. That is what fools have written, what imbeciles commend, what rouges teach and young children are made to learn.
Not to begin to understand his disdain for the bible (or more pointedly, the church), but more, to accentuate his shared understanding that the human heart is capable of corruption—much as institutions or societies on whole.
Yes, the human heart is a powerful thing (too); one that does good for good—or bad purposely for their own good, or not.
The heart is a complex system, behavior the result of much, matter and mystery, what is understood or not—even the person themselves who thinks,
Why did (do) I do that, or “Why did (do) I do that?”
On the other side is that one may not…their conscience seared or calloused rather than “tender”, even child-like is some degree.
Jeremiah the prophet was right:
The heart is deceitful above all things, desperately sick; who can understand it?Who can understand why one does or does not do--even themselves at times--but for mystery of life and living, the one who made the heart of man in that dark place before we each were born.