Yeshaya Perek 2
A running theme of perakim 1 and 2 is that merely doing mitzvos is not enough; the thought, kavanah, is just as important. Hashem demands that “You shall no longer bring vain meal-offerings, it is smoke of abomination to Me; New Moons and Sabbaths (1:13)”. On a basic level, one must have in mind that he is fulfillling Hashem's will each time he does a mitzvah (mitzvos tzrichos kavanah). Yet there is a much deeper element: the effect the mitzvah has on one’s character. One can perform every mitzvah in the book and still not be properly devoted to Hashem. In Vayishlach, before they meet, Yaakov tells Esav 'I lived with Lavan,' which Rashi understands to mean 'I kept all 613 mitzvos and did not learn from his evil ways'. This can be interpreted to mean that keeping mitzvos does not guarantee righteousness - one can do mitzvos for selfish motives. Thus, Yaakov had to emphasize that he had both performed the mitzvos and internalized them fully. Mitzvos are the Divine means of correcting our characters and attaining closeness to Hashem - and as such deserve much thought, focus, attention, and devotion. Rav Shimon Schwab offers an insight on this theme, connected to korbanos.
A korban is made up of two parts; the physical laws governing the animal itself and how it is to be offered, and the mindset of the person bringing the korban. Each type of korban comes with its own specifications as to the gender, age, and species, as well as the laws regarding how it is to be offered and when (if at all) it is to be eaten. However, no less important is the requisite mindset of the person bringing the korban: the korban is offered to inspire thoughts of repentance and genuine introspection. Watching an animal being slaughtered is supposed to make a person stop, think, and internalize the destructiveness of sin.
Adam’s two sons, Kayin and Hevel, were the first people in Tanach who we see offered korbanos. Hevel’s korban was accepted, unlike that of Kayin, leading Kayin kill his brother. The Sforno writes1 that Hevel’s korban was not necessarily physically better than Kayin’s. Both brought the produce of their occupation: Hevel was a shepherd and brought the fat of the sheep, while Kayin was a farmer and offered the fruits of the land. The difference, says the Sforno, was in the two brothers’ mindsets. Hevel was full of thoughts of repentance and purity when offering his korban, while Kayin simply offered his korban without any accompanying mindset ('the daydreaming sacrifice-bringer,' so to speak). Rav Schwab explains that Kayin was simply misguided as to the inner workings of korbanos: he thought that offering korbanos was purely a physical exercise that involved no mental element whatsoever.
Yet, continues Rav Schwab, Kayin was not alone in his mistake. Shaul Hamelech spared the Amalekite animals, despite having been told otherwise by the prophet Shmuel, in order to offer them as sacrifices to Hashem. Had Shaul realized that offering korbanos had a mental, spiritual component, he would never have tried to offer these forbidden animals to Hashem. As Shmuel himself said in reproaching Shaul, ‘Does Hashem want these Olah offerings as in obedience to the word of Hashem?! To obey Hashem’s word is better than a choice offering.’2
Later in history this mistake was repeated. In the generation of the first Beis Hamikdash, the people thought that physical motions of sacrificing would be sufficient atonement. Thus, the prophet Yeshaya rebuked them, ‘Why do I need your numerous sacrifices, says Hashem … Bring your worthless meal-offering no longer.’3 Yeshaya rebuked the people for focusing on the physical element of the korban and ignoring its accompanying mental element.
Yet, by the second Beis Hamikdash, people had learned from their predecessors’ mistakes and focused on the mental element of korbanos – repenting and mending their ways. However, as Rav Schwab points out, the people of the second Beis Hamikdash went to the other extreme. They discarded the physical element and act of sacrificesI and ignored the laws dictating what a korban should look like, where it should come from and how it should be offered, believing that mental spirituality would suffice. Thus, the prophet Malachi reproached the people, ‘You present Me on My altar loathsome food … when you present a lame or sick animal is nothing wrong?’4 One’s ‘mental connection’ is worth very little if it is not mirrored by adherence to particulars of the mitzvah in question.
A contemporary attitude to mitzvos that is prevalent is ‘I’m alright as long as I feel spiritually connected’. Perhaps this is an outgrowth of the selfishness and self-centredness prevalent during the generation that were guilty of the baseless hatred that destroyed the Beis Hamikdash. Having the audacity to redefine spirituality on one’s own terms, whether believing it to be mental or physical, is an act of self-centredness.
 Sforno Bereishis 4:5
 Shmuel Alef 15:22
 Yeshaya 1:11-13
 Malachi 1:7-8