The Book of Vayikra focuses to a significant degree on the various korbanos that were to be given in the Mishkan (Tabernacle), and later the Beis HaMikdash (Temple). A number of these korbanos are known as korbanos nedava (gift offerings). They are not obligatory, however, if a person is aroused to give such an offering, then he fulfils a Mitzo and to do so is considered highly praiseworthy. The Steipler Gaon zt"l asks a penetrating question about the nature of these korbanos nedava. Most Mitzvos are obligatory because Hashem's wisdom decreed that a Jew must fulfill them, thus they are an essential aspect of one's Avodas Hashem. Korbanos Nedava are not obligatory, implying that they are not essential to a Jew's Avoda.. However, on the other hand, offering such korbanos is considered to be a Mitzo, implying that there is some kind of benefit in their offering and that they do have a place in one's Avoda. How can we understand the nature of this kind of Mitzvo?
The Steipler answers this by first addressing another important question in Jewish thought. One of the most fundamental Mitzvos is that of Ahavas Hashem (to love Hashem). This obligates a Jew to direct his emotions in such a way that he develops a strong love of Hashem. How can theTorah can obligate one to have a particular emotion - surely that is beyond a person's control? To answer this problem, the Steipler brings the yesod (principle) of the Mesillas Yesharim (Path of the Just), with regard to the trait of zerizus (zealousness). He writes that just as internal inspiration brings about external actions, so too, external actions can arouse one's inner feelings. Thus, acting in a certain manner can bring about desired emotions.
The Steipler writes that this yesod applies very strongly to the Mitzvo of Ahavas Hashem. We know that an internal love brings one to actions reflecting his love for Hashem and his willingness to ignore his own desires for the sake of Hashem's honor. So too, performing voluntary actions that involve placing Hashem's Ratson (will) before one's own desires, will bring a person to an increased love of Hashem.
With this yesod, the Steipler explains the nature of korbanos nedava. These korbanos provide one with a great opportunity to get close to Hashem by placing Hashem before himself: He forgoes his own needs by exerting a considerable amount of time, effort and money, in order to bring an animal or food offering to the Temple and offer it up to Hashem. Showing such selflessness on behalf of Hashem is a highly effective way of arousing one's love of Him. This explains why bringing korbanos nedava is such a praiseworthy act. However, if the Torah obligated every Jew to bring such korbanos, then their whole purpose would be lost - when one is obligated to give of himself to another, he does not develop feelings of love, rather he feels that he is paying a debt that he owes. Thus, the Torah gives each Jew the opportunity to arouse himself to fulfill an action that will surely increase his ahavas Hashem by making korbanos nedava 'optional'. Yet at the same time, offering such korbanos is considered a great Mitzvo because of its effectiveness in bringing about love of Hashem.
The Steipler writes that this yesod is not limited to korbanos; a person can choose any specific area where he desires to exert an extra amount of effort that goes beyond what is required by law. By 'willingly' giving of himself in one area he can bring himself to an increased love of Hashem. This idea is demonstrated by the following story told over by Rav Yissachar Frand Shlita: He was once given a ride by a seemingly ordinary Jew. In the course of the conversation it emerged that this Jew gave particular emphasis to the Mitzvo of prayer. He had not missed praying in a minyan for several years and even cancelled a vacation to a place when he realized that he would be unable to find a minyan there. Further, he never prayed Mincha or Maariv before or after the ideal time. This man chose one area in which to put in that extra effort and self-sacrifice and in this way he was surely able to arouse in himself an increased love for Hashem. He didn't need to feel obligated to act in this way because it is possible to find heterim (leniencies) to sometimes miss a minyan and not pray in the ideal zman. Yet he chose to express his desire to do Ratson Hashem by being extra careful in the Mitzvo of prayer.
We learn from the yesod of the Steipler, that a key method of bringing oneself closer to Hashem is by doing actions that are not considered obligatory according to the Torah but that are certainly praiseworthy. It is instructive for each person to strive to find at least one area in which he makes that extra exertion in his efforts to get closer to Hashem.
 A korban is normally translated into 'sacrifice' - this is not an accurate translation, in that the root of the word, korban is karev, which means 'come close' the essence of a korban is an act of coming close to Hashem, thus when a Jew gives a korban he does not focus on the 'sacrifice' that he is making by offering an animal to Hashem, rather on the closeness to Hashem that he is gaining.
 Such as Olos, Shelamim and Menachos.
 Birchas Peretz, Parshas Vayikra.
 Mesillas Yesharim, Ch.7.