Banks produce short-term debt for transactions and storing value. The value of bank money must not vary over time so agents can easily trade this debt at par. This requires that no agent finds it profitable to produce costly private information about the bank's loans. To produce safe liquidity...

Banks are optimally opaque institutions. They produce debt for use as a transaction medium (bank money), which requires that information about the backing assets - loans - not be revealed, so that bank money does not fluctuate in value, reducing the efficiency of trade. This need for opacity...