The two goats used in the priestly service must be identical, according to halakha. "The two he-goats of the day of atonement are required to be alike in appearance, in size, in value, to have been bought at the same time." (Bavli, Yoma 62a)
In an article in the Yeshurun journal (1858), Rabbi Samson Refael Hirsch notes that, despite the identical external appearance between the two goats, their fate was different. The two goats used in the priestly service on Yom Kippur are a representation of the two choices a person has: one choice brings him closer to God, and the other leads him to heAl (azazel). The different identities of the two goats make it abundantly clear to a person that neither external circumstance nor his own life story have the power to force him to choose the path he will take in life. The person himself must make the choice and he has the power and ability to choose the correct path. HaRav Hirsch points out that the use of goats is appropriate for the occasion of the priestly service. Just like a goat becomes attached to a specific shepherd and withstands the temptations of other, competing shepherds, so also the People of Israel, the stiff-necked, stubborn people are able to withstand the temptation of sin. The ceremony of the scapegoat (se'ir la'azazel) highlights the outcome of a person's choice – will he achieve holiness or, God forbid, be smashed to smithereens against the rock.
HaRav Hirsch follows the same train of thought in his commentary on the Torah and stresses that the identity of the goats symbolize the choices a person has in life.
"The two goats mentioned here describe two figures. At the beginning they are identical but, at the entrance to the Mikdash, their paths separate… the one who was chosen by the lot to be for Hashem, will be slaughtered by the sharp knife in the Mikdash; yet he will be received in the holy vessels of the Mikdash and from there will be brought into the most sacred site, the Holy of Holies. In contrast, the one who was chosen by the lot to Azazel, will be alive without any change. Yet, he will not enter the Mikdash, he will be taken away from civilization, and be led to the wilderness. By turning his back to the Mikdash, the goat retains his own self-identity and will end his life in the desolation of the wilderness… We have the choice – either to personify the 'goat for God' and to stand up to all the internal and external threats that tempt us away from God, or to personify the 'scapegoat' and to use our strength to refuse to listen to God's voice…"
(Hirsch Commentary, Leviticus, 16:10)