Sheep

The Midrash describes the Jewish people as G-d's "sheep" [Shir HaShirim Rabah 2:16], as an expression of their total dedication to G-d, like sheep that follow their shepherd unquestioningly.

Yaakov exemplified this level of dedication while he worked for Lavan, remaining loyal to G-d's commands despite the spiritually alien environment.  Thus, to hint to Yaakov's dedication, G-d rewarded him with wealth that came about through amassing sheep.

However, when Yaakov returned to confront Eisav, he did not stress sheep as his most important acquisition, but rather, oxen [Vayeitze 32:6].  Yaakov was hinting: "Because I am dedicated to G-d like a quiet sheep, therefore I have G-d's might behind me, so I will be as strong as an ox against you."

This teaches us that, in our observance of mitzvos we should be utterly humble towards G-d like a sheep; but when fighting the forces that oppose Judaism in the outside world, we cannot stand by sheepishly and watch Jews be drawn away from their heritage. Rather, we must fight for Jewish values with the strength of an ox.

Source: Based on Likutei Sichos of the Lubavitcher Rebbe: Gutnick Chumash