Bob covers John 1: 19-31 in his Bible commentary series. He states that a lamb was not a "scapegoat" in terms of Jewish animalistic sacrifice for the propitiation of sins (using an RC Sproul clip to explain). Then Bob gives various justifications for the use of a sacrificial lamb, since it seemingly violates our intuitive sense of justice.

Mentioned in the Episode and Other Links of Interest:

The previous episode in this series, i.e. BMS ep 334, Installment 4: the Word Became Flesh.
The RC Sproul sermon on Jesus as the Lamb of God.
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Ep. 339 An Interdisciplinary Commentary on the Gospel Accounts of Jesus Christ: Installment 5, the Lamb of God