One example of this is exemplified in the expression חומד לב רואה עין, the eye sees and the heart lusts. This means that by placing images of desirable things into our mind (through the eye), we activate the heart to desire it. The same applies to hearing—another window into the brain. When a person hears that so-and-so has done him wrong, his heart is activated to loathe that person.
In the same vein, the Torah tells us here that when a person places words of Torah into his mind, his heart will become activated to love Hashem with a great love.
How does this happen? First, the words of Torah themselves carry the names of HaKadosh Baruch Hu, and when they enter the mind, they give birth to ahavas Hashem. Second, by constantly repeating words that bring him to love—that is, by saying how much Hashem loves him and does good for him—it will awaken in him a burning love for the Ribbono shel Olam in return.
A Constant Mitzvah
From the words of the Ohr HaChaim HaKadosh, it seems that we are being asked for something more than the mere הלב על שליט מח..., as the regular emotions of a person fluctuate. Love (or another emotion) is awakened, but it soon subsides. The emotion of love for Hashem, however, is a constant mitzvah—and it therefore requires us to constantly place the words on our hearts, constantly awakening ourselves to love Hashem. For every word and every thought has the power to awaken it. And when a person persists at it, his love for Hashem compounds in quality and quantity until his heart is transformed into a heart that loves Hashem with all the qualities enumerated in the pasuk of V’ahavta ... (with all your heart, with all your soul, and with all your resources), and he able to thank and love Hashem לו מודד שהוא ומידה מידה בכל, no matter with which measure Hashem behaves toward him.
We see from here that a person is obligated—according to the Torah—to constantly tell and retell himself the goodness that Hashem does for him and the love that He displays toward him, for this is the only way to awaken a constant love and thus adequately fulfilling the mitzvah of ahavas Hashem.
