John Piper on RC

I have much respect for John Piper (heard him speak when I was in England while he was there on a speaking tour).

I'm glad that he thinks justification is the key issue he would confront the Pope with (though he thinks there are other issues in which RC gets it wrong, e.g. papal authority, the nature of the mass, etc.). But again, I just cannot accept his view of justification as one in which Christ's righteousness is "imputed" by "faith alone".

I should also say that I do wholeheartedly accept the claim justification by faith... we are justified by faith indeed! God is the efficient cause of my being justified as well as my even having faith.

But nowhere in Scripture do I find the notion of justification by imputation (where it is solely an extrinsic, external matter) nor of faith alone (and the epistle of James tells me otherwise).

Will someone please let me know whether I've erred about this and why, because this is a huge separation between me and the magisterial Reformers--which would then be a short hop, skip, and step to RC.

(I've read Piper's response book to Wright's book on justification; and so far, Piper's case doesn't seem very convincing... sigh...)