In my Dynamics of Biblical Change lectures, Paul Tripp used an illustration that shed some light on the TR vs. Federal Vision controversy. With a nod to David Henderson's Culture Shift, he argues that being Biblical means that Scripture and its themes and nature as covenant story (vs. being frustrated with Scripture that it is a poorly organized Systematic Theology text) forms the "time signature" and "key signature" of our lives. In order to be faithful to Scripture and to Scripture's God, we must listen to the time and key signature and then, like a good jazz ensemble, look to the covenant community as we improvise making "covenant jazz" in faithfulness to the formative and authoritative nature of Scripture. If we are arguing over the score instead of making music, we have missed the nature of Scripture and missed the purpose, to make covenantal music to the glory of God and the spread of the kingdom.
The TR crowd is quibbling over an "authoritative" constructed score (read: WCF) while Federal Vision is improvising using the time and key signature of Scripture (read: covenant). The "heresy" of FV is that they are improvising. The "heresy" of the TR's is that they are not making covenant music. They are arguing over the score in a way that abuses the Confession and misses the covenantal story of the Scriptures.