Meshech Chochma(Vayikra 19:18): Bereishis Rabba (41:1): A tzadik flourishes like a date palm… Just as a date palm and cedar tree have desires also tzadikim have desires. What are their desires – it is for G‑d…. Rav Tanchum said that there was a date palm in Chamaso which did not give forth fruit. A palm tree gardener passed by and commented that this date tree is longing for palm tree in Jericho. Once the two were grafted it bore fruit. The key to understanding this medrash is from the tradition that the yetzer harah does not have an influence except on which the eyes see (Sotah 8a). Lust for material things only is aroused by what the eye sees and then the heart desires(Bamidbar Rabbah 10:2). Similarly Megila (15a) says that the mere mention of the name of Rachab (who was very beautiful) caused a person to be sexual aroused. But that was only if the person knew what she looked like. However what the eye hasn’t seen the heart doesn’t desire.
In contrast the lust of tzadikim is not that way but comes from the power of the mind… Their desire is solely for spirituality and getting close to G‑d and not for material things. This is stated in Shemos (33:20): No man can see me and be alive. Thus we can understand the lust of the date palm and the cedar tree to which tzadikim are compared. It is not based on material desires. Therefore we see that the date palm had desire for that which it couldn’t see. The tzadik has gained control over his material nature and now has desire for that which can’t be seen – which is G‑d. This is also the proper understanding of “You shall love your fellow man as yourself I am G‑d.” Just as you have been commanded to love G‑d even though He hasn’t appeared before you – similarly you shall love and value every single Jew – even though he is so far away from you that you have never seen him.