Sforno on Numbers 7:13/ספורנו על במדבר ז׳:י״ג

1'וקרבנו קערת כסף אחת, וגו; each one of the princes offered all these components as part of his offering. They comprised: a burnt offering, עולה, a gift offering, מנחה, a sin offering, חטאת, as well as peace offerings, שלמים, and incense, קטורת. The reason why the Torah does not simply lump all these offerings together but tells us separately, 12 times what each prince’s offering consisted of, is that each one had intended thereby to atone for all the sins he was aware of that members of his tribe had committed, had been guilty of. Each prince performed the סמיכה, the act of placing all his weight on the animal becoming the sin offering on behalf of the members of his tribe guilty of sins requiring such a sin offering to atone for their sins. This was a regular procedure when communal offerings were being brought.