Oil represents chochmah (wisdom) which, in turn, expresses the theme of selflessness (bitul). The selflessness imparted by the oil is required for both aspects of the flame.
The dark flame radiates from the wick, which corresponds to the body and Animal soul. Through the process of self-abnegation and surrender the oil is drawn. Through the smooth flowing of the oil, the dark flame of enthusiasm can burn for a considerable amount of time. If the oil of selflessness does not flow properly, the flame does not last.
At the higher level of the bright flame the oil is also essential. The purity of the radiance of the flame of spirituality depends on the purity of the oil of selflessness. It flows from the highest spiritual levels and brings about a deep, mystical humility.
THE SPIRITUAL EFFECT OF 'OIL'
The Dark Radiance
So the oil is what causes the flame to bond with the wick. This enables the flame to burn a long time and also produces the two colors of white and black flame as explained above. The same is true regarding the soul and the body. Through the oil, which refers to chochmah,1 the soul bonds with the body in all its faculties,2 and this bond lasts a long time.
Now, as is known, chochmah of the divine soul is termed koach mah,3 "the power of selflessness" — utter abnegation in relation to the divine ayin4 which transcends reason and understanding. Subsequently, chochmah spreads its force into binah, which represents comprehending something divine. Chochmah and binah are the yud and the hey of the soul,5 as is known. The potential power in the "spark" in every Jewish soul, even the most lowly, to surrender its self and to be utterly moved before G‑dliness, is called the power of selflessness of the soul. It is this which is termed "oil" — like oil, which flows in the wick — the body — in order to arouse in it too the quality of abnegation of its sense of ego and its coarseness, so that it should submit and be abnegated and be utterly contrite. This is the abnegation of the self to that which is beyond.
Thus as we see, sometimes a person's heart will be quelled, leaving its material coarseness. Its free ranging desires will fall away, in the face of intimations of the Living G‑d, arousing the person to true teshuvah from the inner depth of his heart. This is "the broken and contrite heart."6 This is from the consumption of the "wick" in the Divine radiance by means of the oil, on account of the power of mah (selflessness) which it imparts.
This "selflessness" is due to good oil, which flows properly in the wick. If it does not flow properly then the Divine radiance does not cleave to one's mind and physical emotions and it is quickly extinguished.
Thus, this [good] oil causes the burning of the dark color of the flame,7 the "flame of Y-H." Gradually this flame consumes the wick, i.e. the body, so that it too should be absorbed in the Divine radiance, the radiance of spiritual ecstasy, with flames of longing, lasting a long time.
The second effect of the oil is the clarity of the higher "white" flame of the soul which is called bright radiance.9 This depends on the purity of the oil, which is drawn into and is consumed by the flame.
This [double effect] is because the power of selflessness — termed "oil" — has two levels. The first is the way it flows from concealment to revelation. This causes the quelling and abnegation of the [material] self before G‑d,10 within the actual body, so that in his very physicality the person has a contrite spirit.
The second level relates to the manner that the power of selflessness is manifested at its root, in the actual divine ayin, as it is written "chochmah appears from ayin," literally from the spiritual level of ayin. For every soul contains a quality of utter abnegation before G‑dliness, to become ayin, literally "nothing," and not just to transcend one's physical self. This is a kind of intense meekness and humility in the very essence of one's being, until one's soul is really "as dust to all,"11 not feeling any importance in oneself at all in everything one does. (This is called in Yiddish "nishtkayt, er is gor nisht be'etzem"[nothingness, he is utterly nothing].)
This is the meaning of the verse "in the heart of every wise of heart, I have placed chochmah,"12 and "He gives chochmah to the wise,"13 and "let my soul be as dust"; [by which] certainly and spontaneously [will be fulfilled the request59] "open my heart to Your Torah."
The Power Of Humility
It is through this humility that man elicits the supernal radiance of the inwardness of chochmah,15 revealing the radiance of Ein Sof,16 which shines from the concealment of the Essence17 [which is] in each soul, with the quality of the very essence of the light. This is the light sown for the Supernal tzaddik, mentioned above,18 and is called bright radiance, which shines with the ecstasy of one's whole essence expressing ahava b'tanugim with kelot hanefesh.19 Another mode of expression might be that of teshuvah with true self-sacrifice.
This [humility] derives from the consumption of the oil, from the fact that it is drawn into the flame, [thereby expressing] lowliness and humility, for the upper flame draws the oil [and consumes it, which in human terms] enables one to reach the essential ayin of G‑dliness. This causes the brightness of the upper flame — due to the purity of the oil, which is a manifestation of the depths of true lowliness and humility, not being conscious of one's own self at all in any way.
Thus, deeply hidden in the inner quality of koach mah [deriving from the "oil"], are the two kinds of radiance of the flame, the bright radiance and the dark radiance. By means of selflessness they emerge from concealment to be revealed in the soul.
(The same is understood of the "general soul"24 — malchut of Atzilut which also has two kinds of radiance. As it says in the Zohar,25 explaining the verse "G‑d, do not be silent,"26that the lower radiance calls continuously to the higher radiance.27 This is sufficient for the wise.)
The operation of a well-structured lamp requires oil. The same applies to the soul. In order to attain any sort of G‑dly inspiration, whether the sublime stage of self-surrender in delightful love, or the transformation of negative emotions to focus on G‑dliness, one must use spiritual oil. Oil refers to chochmah of the G‑dly soul, which itself expresses the theme of bittul (selflessness), and is concealed within the binah, the G‑dly comprehension in the soul. This causes the body to subjugate itself to G‑dliness as well.
We observe empirically that one's corporeal heart can suddenly experience complete subjugation when the person understands a Divine reality. This arouses the person to total teshuvah. He is then termed "broken-hearted" (Psalms 51:19) and all self-importance he may possesss immediately dissolves. This is caused by healthy oil, which is drawn after the wick. When the oil is of inferior quality, the wick is unable to absorb it and is swiftly consumed.
The second (aforementioned) benefit resulting from the oil is the emergence of a pure flame, or radiance. In human terms, this refers to the essential light of the soul.
Thus, the two levels of the oil of the soul — chochmah, selflessness — correspond to the two aforementioned benefits of a well-structured lamp:
1) Abnegation of the "self" of the body — paralleling the darker radiance which depicts the flame's cleaving to the wick and gradual consumption; 2) Essential abnegation of the soul, also sensed by the body (termed "wick" or chomer, "matter") to illuminate with a sensation of "may my soul be as dust," "giving wisdom to the wise" (i.e., selflessness to those who sense it) — paralleling the illuminating radiance that results from healthy oil.
Hence, these two colors are present in G‑dly comprehension, which in turn, reveals them (similar to oil, which, as mentioned earlier, contains the two colors of the flame).
The 'Holy Anointing Oil' used in the Temple for the vessels and Kohen Gadol was made from olive oil and various herbs and spices. It is explained in Shemot 30:22-25.
It is not the same oil used for anointing Kings of Israel. This oil is called 'Shemen Afarsimon',which is mentioned in the Tosefta on Sheviyit and also in Yerushalmi Sheviyit.
(תוספתא, שביעית פ"ז ה"י; ירושלמי, שביעית פ"ט ה"ב; לח ע"ד)
Here is a link in Hebrew which gives a good explanation of Shemen Afarsimon.
According to the Roman botanist, Paulinus, the Afarsimon tree had a unique oil and only grew in the territory of Yehuda. This would suggest why Shmuel was directed to the Afarsimon oil for anointing Kings of Israel. Kingship was intended to lay only with Yosef and Yehuda.
The word Moshiach means “anointed”. In the olden days before a king assumed office, he was anointed with oil. So too, there will come a time in the future when a Jew who is both learned and a descendent of King David will be anointed as a king and will rebuild the Temple in Jerusalem and gather all the Jews to Israel. This King is called Moshiach.
In the days of Moshiach, there will be no wars or famine and everybody will have all they want. The Jews will be able to sit and study Torah in peace and the whole world will be full of the knowledge of G‑d. The generation we are living in is the generation just before the coming of Moshiach and we eagerly await his coming every day. We also do lots of mitzvotto speed up the coming of Moshiach.