Love is not irrational. Love is an emotion. Emotions are the perception (brain's interpretation) of a feeling. Feelings are sensations. The issue that is irrational is the manner in which our brain interprets an emotion. We have a number of sensations, increased heart rate and sweat production among others, that are used as we interpret emotion. An excellent example, Dutton and Aron (1974), found that men crossing a high bridge found the woman at the other end more attractive than men crossing a low bridge. This has been shown to work for the emotions as well. One study found that following or during an intense bike ride a person would respond more aggressively to negative actions, but I forget the study. Studies that are interesting to look at typically deal with pain elicited aggression and excitation transfer (although imo cognitive explanations are a waste of time, you should focus on the physiological reality that arousal level determines level of emotion, and stimulus determines type of emotion.)
So love of wisdom refers to the interpretation of sensations associated with or attached in some way to wisdom. So, love of wisdom may be looked at in a number of ways.
1) The feeling being interpreted as the calm love associated with feeling immediately following sexual relations that does not include anything leading to guilt. So love of wisdom = the calm feeling of wisdom.
2) The feeling being interpreted as the devoted love associated with the desire to protect at all costs. So love of wisdom = Care in wisdom.
3) The feeling being interpreted as the lust associated with the act of love. So love of wisdom = Overwhelming desire for wisdom.
Other interpretations may exist, these were just a few simple ones to give examples.