From Rabbi Moshe Sofer, Derashos Chasam Sofer, Vol. II, “LiShavuos,” 291a
From “The Vision of Eden: Animal Welfare and Vegetarianism in Jewish Law and Mysticism" (Orot 2003), p. 316
The verse states: “When you bring a new meal-offering to God on your festival of Shavuos (Weeks)...” (Numbers 28:26). The initial letters of the Hebrew words “a meal offering to God” spell the word chalav (milk).
This alludes to the custom of eating dairy foods on the festival of Shavuos mentioned in the Sefer HaRoke’ach. We see that it is beneficial to consume animal foods in order to elevate the holy sparks they possess to the human level. Yet if it would be sufficient to eat butter and milk, without having to slaughter a living creature, this would be far better. Thus did Adam conduct himself before the first sin. Afterwards, the human soul no longer possessed the requisite spiritual power to elevate the holy sparks by consuming dairy foods alone, without slaughtering the animal and spilling its blood—for this act accomplishes the release of the animal’s soul. Otherwise, the holy sparks could not ascend. Although after the first sin, animal slaughter still was deemed to be wrong, it was permitted to Noah after the Flood. However, on the day of the Giving of the Torah, the Israelites regained the spiritual level of Adam before the first sin. Therefore, it was sufficient to consume dairy foods, without slaughtering animals, and the holy sparks were elevated through milk.