Sean Michael Lucas posted this email last month on his blog; I saved it and just now got around to reading it. He seeks to explain to a correspondent how God can make a "promise" that's signed and sealed in a covenant, and yet for many people, it is not effectual. I've had the same question, too. It's a helpful answer, I think.
Even though I disagree with the paedobaptism argument, I want to grow in understanding their view and arguments.
Next week (Lord willing), I'll post an interview that seeks to explain how a credobaptist views the continuity and discontinuity of the covenants.