Chazal (Niddah 9:) tell us חלב ונעשה נעכר דם, "blood becomes spoiled, and turns into milk." The origin of milk is blood, which transforms itself into milk. It is forbidden to eat blood, so why is it permissible to drink milk? It must be that when it turns into milk, the blood disappears. The Brezhaner Rav zt'l says that this symbolizes teshuvah. When we improve our ways, there remains no sign of our past sins.
The Yerushalmi (Rosh Hashanah 4:5) states, "By all korbanos it states לחטאת עיזים שעיר, a goat for a sin-offering.' But by the korbanos of Shavuos it states עליכם לכפר עיזים שעיר, 'a goat for atonement.' חטא isn't mentioned because, on Shavuos, no one has sins. Hakadosh Baruch Hu tells Bnei Yisrael, 'Since you accepted the yoke of Torah, it’s as though you never sinned your entire lives.'"
The Torah writes (Shemos 19:4) על אתכם ואשא נשרים כנפי, "I carried you on eagles' wings." The Yismach Yisrael (Yisro 6) explains that an eagle sheds its feathers and grows new ones every year, as it states (Tehillim 103:5) כנשר תתחדש נעוריכי, "Become new, your youth, like an eagle." Rashi writes, "Like an eagle that replaces its feathers and hair yearly." Similarly, the Torah tells us that Hashem carried us on eagle’s wings to remind us that we should constantly change and improve our ways.
