"God's angel appeared to Moses in the heart of a fire, in the midst of a thorn-bush." (Ex. 3:2)
Why did God choose a sneh, a thorn-bush to reveal Himself to Moses?
A Cure for Fever
The Talmud (Shabbat 67a) prescribes a peculiar procedure for those suffering from a high fever. The patient is advised to take a thorn-bush, and each day make a cut in it using an iron knife. When cutting the bush, he should trim it near the ground, and say:
"Thorn-bush, thorn-bush! The Holy One did not let His Presence reside in you because you are the greatest of all trees, but because you are the lowliest."
What do thorn-bushes have to do with fevers? What is the purpose of this strange procedure?
Circumstantial and True Humility
Rav Kook wrote that there are two forms of humility. The first type could be called 'circumstantial humility.' Due to infirmity, poverty, or some lack of talent, intelligence, social standing, etc., a person may feel vulnerable and insignificant.
However, this is not genuine humility. Should circumstances change, newly-found strength or wealth or prestige may very well delude one into believing in his own prominence and self-importance.
True humility comes from a different, more objective source: awareness of our place in the universe. This humbleness is independent of the vagaries of life's circumstances. It is based on recognition of our true worth, on insight into the essence of the soul, and a clear understanding of the nature of reality.
Unfortunately, the fickle nature of the human mind allows us to be easily deluded into ignoring anything beyond our own egocentric world. How can we escape such delusions?
This trap may be avoided by recognizing the transitory nature of circumstances. Poverty, sickness, and so on, have the power to make us aware of our intrinsic vulnerability. Awareness of our inherent potential for weakness leads us to properly evaluate our true worth, and thus attain genuine humility.
The Lesson of the Thorn-bush
By all criteria, the thorn-bush is a lowly and unimportant plant. It grows in barren locations, providing neither food nor shade for others. It even rejects interaction with other living things by means of its prickly thorns. Yet, precisely because of its isolation, the thorn-bush may deceive itself into believing in its own greatness. Therefore, the Sages advised cutting the bush down to its very roots. We trim away all the superficial aspects, leaving only the bush's essential worth - its roots, its connections to the rest of the universe. God placed His Divine Presence on the sneh not because of its sense of self-importance, but because of its innate lowliness - the spirit of true humility which remains after the bush has been trimmed to the ground.
The thorn-bush procedure recommended by the Talmud enables the suffering individual to recognize the purpose of his illness: attainment of sincere humility. This trait is the remedy for all strange fevers and delusions.