Andrew, here is a brief summary of what James is explaining.

The struggle around interpretation is not imposed upon Scriptures, but something that happens within them. For a rather important example, this session looks at the different interpretations offered by Jeremiah and Ezekiel around the question of God’s involvement with child sacrifice. We’ll see how the Binding of Isaac passage from Genesis 22 reflects the movement away from understanding God as a God who demanded the sacrifice of the firstborn.
The Marcionite and fundamentalist temptations were faced by the authors and editors of the Hebrew Scriptures themselves. ? The people we now call the people of Israel had as a regular part of their basic culture the sacrifice of firstborn children.
Jeremiah, a northern prophet, offers a pre-Marcionite interpretation when he says that it was not YHWH that commanded child sacrifice but another god.(Jeremiah 19:3-6)
Ezekiel, a fairly conservative Temple priest from Jerusalem, seems to have the fundamentalist temptation. He is saying that yes, child sacrifice was commanded by YHWH, but it was so people would find it so awful they would give it up. (Ezekiel 20:23-26)
Both prophets faced the same problem yet despite their different solutions they were both dangerously secularizing – they both agreed that true religion did not involve child sacrifice, contrary to their religious contemporaries.
The story of circumcision as a covenant of peace inserted into the narrative about Egypt may have been part of a history of the interpretative dealing with the moving on from child sacrifice.
The passage called the Akedah or the Binding of Isaac (Genesis 22:1-19), may have been an edited version of an earlier story in which Isaac was sacrificed. So the current version, as it appears in our Bibles, reflects moving on from a God who demanded the sacrifice of the firstborn.
Does that help?