Swords into Plowshares

In AGOT Catelyn XI, at the council at Riverrun, we have the following passage.

The hall was very quiet when Catelyn finished speaking.

"Peace," said her uncle Bryndon. "Peace is sweet my lady ... but on what terms? It is no good hammering your sword into a plowshare if you must forge it again upon the morrow."

Swords into plowshares is an extremely famous biblical metaphor from Isaiah 2-4: "He shall judge between the nations, and shall arbitrate for many peoples; they shall beat their swords into plowshares, and their spears into pruning hooks; nation shall not lift up sword against nation, neither shall they learn war any more."

While based in medieval Europe, I think GRRM usually takes great care to avoid explicit biblical language, or other examples where characters make references to literature in our own real world, in order to keep a certain distance between his world and ours. As in real history, Knighthood in ASOIAF is still something of religious order, as Knights are anointed by the Faith of the Seven.

I would call this not a blunder, but just a minor tonal inconsistency that took me out of the story for a moment. Anyone else ever notice this, or other examples of it type?