The Medrash Tanna D'bei Eliyahu [6/ 17] says that a person might say that he will do 'disgusting things' [דברים מכוערים] and then bring a korban mincha [flour offering] because of the love that he has for Hashem. Is this love? He will do terrible things and then show his love for Hashem and bring a korban? It doesn't even say that he wants to atone for his sin. What is going on here?
The Medrash continues that Hashem answers: My son, why didn't you mix your actions with Torah and maasim tovim? The oil we mix with the flour offering represents Torah and good deeds as the pasuk says לריח שמניך טובים שמן תורק שמך - "On account of the fragrance of your fine oils, your name is flowing aromatic oil".
This implies that Hashem isn't bothered by the fact that this person is planning to sin and then bring a korban but just wants to make sure that his sins are mixed with Torah and maasim tovim.
Explained the Rebbe Shlita as follows: The Pnei Menachem [תשנ"ד ליל שב"ק ד"ה כ"ק] says that the tshuva of Adam Harishon was insufficient. Chazal teach that he separated himself and became an ascetic and פרוש for 130 years. This was not the way to go. Man was created to be PART of this world, to be ENGAGED, not to separate himself. The Kotzker says on the pasuk ואנשי קודש תהיון לי - You should be holy PEOPLE to me. Hashem has enough angels, he wants holy human beings. People who eat, drink and sleep.
The gemara calls a nazir sinful because he voluntarily denied himself the pleasure of wine. The Mezritcher Maggid said א קליינע לאך אין דער גוף א גרויסער לאך אין דער נשמה- A small hole in the body, a big hole in the neshama. The Rambam [Deyos 3/1] emphasizes that one should not be a פרוש someone who denies himself the pleasure of this world [see there at length].
That is what the Medrash we quoted at the outset means: The "disgusting things" [דברים מכוערים] this person plans to do is to separate himself from this world. To be an ascetic, to fast, to deny himself sleep, maybe not get married etc. etc.
Hashem says - NOOOOOO! It is OK to great to have a side that doesn't overindulge in the pleasures of this world but it is forbidden to completely separate yourself. You must be engaged. Learn Torah which is all about sanctifying and fixing this world. Engage in good deeds, help people, call the old widow in the neighborhood and ask how she is, babysit for your nephews and nieces, spend Shabbos in a home for the mentally and physically challenged. Hashem wants our Torah and Maasim Tovim, not our self-inflicted suffering.
That is what the Torah means when it says about Hevel והבל הביא גם הוא מבכורות צאנו - Hevel brought "even him" from his sheep. What does it mean when it says גם הוא - even him?
It means that he brought himself with all of his physicality and sacrificed everything to Hashem. He didn't starve himself or torture himself in other ways. He brought "even him" - his complete human self and dedicated it to Hashem, in addition to the animal offering that he brought.
[Melave Malka Parshas Bereishis 5760]