The Gemarah states that the words ‘acharei levavchem’ is referring to heresy/minus. It would seem that these foreign beliefs are something generally rooted in the intellect of man rather than his heart. Why then does the Torah refer to it as something associated with his heart rather than his mind?
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Al derech drush, Gemara in Sanhedrin says Moshiach comes when entire generation turns to minus, and learns this out from passuk that says kulo hafach lavan tahor hu, the whole body turns white with tzaaraas. One can read the word lavan as liban, hearts. That would explain why here also we darshen the word livavchem to be referring to minus. Furthermore, the Gemara in Sanhedrin states that Adam harsihon was a min, and proof of this is because HaShem said to Adam, ayeka, an natah libcha, where has your heart taken you.
ITS COMMON SAYING
ONE CAN HAVE A SHARP MIND [THINKING
AND A WARM HEART [LOVE]
what means i love you with all my heart?
the heart is the monitor of the mind
Rav Dessler explains that the mind is “bribed” from the heart. The perfect example of this in the search of the existence of God. When a persons middot and wills dont “fit” with the existence of a God so the evil in his heart will bribe and alter his logical reasoning and maskanot in the search for God. So it’s the heart that affects the intellect in the end of the day.
Another idea that Rav Dessler explains is that we can only fathom Hashems attributes if we ourself have those same attributes. The classic example is that unless a person is truly altruistic and a true bal chesed he cannot fathom that Hashem created the world for a truly alturistic purpose. A person who only does acts of kindness for his own self gain will think the same of Hashem and will believe that Hashem has some suet of egotistic gain from the creation. So you that only thru tikkun hamiddot in the heart we can begin to comprehend Hashems middot.
We have already seen (10a) that the heart is referred to as “mekom binah,” the place of understanding so this isn’t a new idea. We don’t necessarily fully understand the Torah’s “symbolic biology.” But as a previous commentor alluded to, in both Torah and secular thinking, love is said to come from the heart. Yet, biologically, all the heart really does is pump blood through our veins.
This doesn’t answer the question, per se, but at least opens the door for all of the other answers.