POST # 100 (Less than a Month!) Daf Yomi - Yoma 59 - Prosecutors and Defenders do not Mix

The Gemora learns from a passuk that blood is given for atonement and not for מעילה (using hekdesh for your own purpose). There is an argument in the rishonim if this is only an exclusion for the obligation to bring a korban, yet there will be a transgression or it is excluded completely.

Reb Yosef Engel brings a Meiri that explains this halacha. Sprinkling of the blood on the mizbeach is a סניגור - a defender for Klal Yisroel. The sin of מעילה is akin to a קטיגור - a prosecutor and hence the two cannot mix.

שערים מצויינים בהלכה brings a similar illustration to this. The Gemora stated above (20) that in a year there are 365 days and השטן has a numerical value of 364 to signify that the Satan does not have permission to prosecute or act against Klal Yisroel on Yom Kippur which is the ultimate day of atonement. The two cannot mix.