The central offering in the daily Temple service was the Tamid, an offering of two lambs in their first year. One lamb was offered just after daybreak, at the start of the day's service, while the second lamb was offered in the afternoon, at its conclusion. The sheep were purchased using half-shekel coins collected from the entire Jewish people.

Why was a sheep used for the Tamid offering, and not a more impressive offering? Why use only young animals, less than a year old? 
 
(Note: Maimonides wrote that offerings are chukim, Divine statutes for which we do not know the reason. Yet that assertion did not deter scholars throughout the ages - including Maimonides himself - from suggesting possible reasons to explain various details of the Temple service.)

Bulls and Sheep
 

Some Temple offerings are bulls, while others are sheep. A bull is generally a peaceful animal and a productive worker. But on occasion a bull can be suddenly transformed into a terrifying force of danger and destruction. For this reason, a bull is an appropriate offering when one seeks to atone for a life that has fallen tragically into a serious state of ruin and disaster.

Sheep, on the other hand, provide a suitable offering when the issue is not one of destructive behavior, but rather a general spiritual decline and an indulgence in materialism. The peaceful but mundane sheep are a fitting metaphor for our daily struggle against the negative influences of over-involvement in worldly matters.

With regard to the Jewish people as a whole, one cannot speak of widespread corruption and moral decay. The Tamid offering, purchased with funds from the entire nation, does not atone for extreme and unusual vices of certain individuals. Rather, it is meant to meet a general need of the nation: to uplift our lives from the spiritual poverty of a materialistic existence, and engage our aspirations for a life rich with meaning and holiness.

Yearlings

But why use sheep in their first year? Unlike older, often ornery beasts, these young sheep do not symbolize a life that is dominated by self-centered materialism. Since the intrinsic holiness of the Jewish people does not allow worldly influences to be etched deeply into the nation's soul, the Tamid offering is best represented by young, relatively innocuous animals.

(Adapted from Olat Re'iyah vol. I, p. 130)