פּירוש אויף ויקרא 5:9

והזה מדם החטאת AND HE SHALL SPRINKLE OF THE BLOOD OF THE SIN-OFFERING [… AND THE REMAINDER OF THE BLOOD SHALL BE WRUNG OUT] — In the case of a burnt-offering of a fowl Scripture requires only the wringing out of the blood (Leviticus 1:15), whilst in the case of the sin-offering it requires sprinkling and wringing out: standing quite near to the altar, he grasps the nape and makes the blood spurt out and thus the blood spurts forth in a jet and goes in the direction of the altar (cf. Zevachim 64b).

והזה מדם החטאת; he takes hold of the body of the bird and sprinkles from a distance, squeezing out the rest of the blood; if the offering is a total offering, there is no sprinkling of the blood; all of it is simply squeezed out. (Leviticus 1,15)

For its sake. This was explained above (Rashi 4:24) regarding the sin-offering of a leader. Rashi repeats it [here] because it is dealing with bird sinoffering and above it is dealing with an animal sin-offering, and [one cannot learn from the other because] they have dissimilar aspects. Therefore, he repeated the explanation here.

חטאת הוא IT IS A SIN-OFFERING — These apparently redundant words intimate: if the sprinkling and wringing of the blood are done for the purpose of (i.e. having in mind that it is) a sin-offering it is valid; if it is not done for this purpose (i.‎e. that the officiating priest has another sacrifice in mind) it is invalid (cf. Sifra, Vayikra Dibbura d'Chovah, Chapter 18 9 and Rashi on Leviticus 4:24).