The power (Vermögen) of understanding presupposes the power of love (Mögen) and not the other way around. You can only what you will: you are only able to understand that which you are able to love. Understanding is not – or need not be – a total comprehension, possession, grasping without a remainder that which is to be understood, but a movement towards the other, towards that which remains to be understood but perhaps never totally grasped.
There is, of course, the kind of "cultivation of intimacy" that ensures a total merging of horizons, because the act already presupposed a shared horizon in the first place, a common code.
But love is – or can be – judgment. Love does not "evaluate" but it judges, having "an idea" of what the other could be, has been or may still become, beyond that which he or she is at the moment, beyond all the deeds and symptoms and indications.
Such an "idea" is – or need be – nothing determinate, not a specific content, not a "logos" in the sense of definition, but an indeterminate "possibility" (Möglichkeit), a movement towards that which is "lovable" in the other (be it human or not, animate or inanimate), but not as some "reason" – love is not a matter of "reason" or "reasons".
"I love you because..." is a horrible way to start.
P.S. I don't make references here to Heidegger's texts, for example, and I am not offering any kind of interpretation of his thought on Mögen and Möglichkeit. This quick note, written on a summer morning in a small cottage by the sea, listening to birds singing, is rather intended as a working hypothesis and thus a beginning of a dialogue to come, an incipit of understanding.
P.P.S. I wrote that "you are only able to understand that which you are able to love", but I must add that the ability to love does not exclude actual hate – or frustration, or disappointment in the status quo.
P.P.P.S. (July 1) Instead of "hate" I should probably have written "anger".
"Angry young men", for instance, are those who have a sense of injustice, and that implies a love for justice, even when justice remains beyond presence (epekeina tes ousias).