I return every once in a while to the relationship of faith to obedience.  Daniel Kirk bangs this drum regularly, too.

To my mind, there can never be enough voices emphasizing that these are nearly synonymous for Paul and not at all in opposition.

In his essay in Four Views on the Apostle Paul, Luke Timothy Johnson puts it like this:

Scholars debate the difficult expression pistis Christou.   Should it be taken as believers’ faith in Christ or as Christ’s faith in God?  There are strong reasons for holding that in some key passages—above all in Rom. 3:21-26—Paul speaks of the faithful human response of Jesus to God as an essential dimension of his sacrificial death.  The expression “obedience of faith” in Romans 1:5 and 16:26 indicates how Paul understands the equivalence between the two terms, and the development of the statements made concerning faith in 3:21-26 in terms of obedience in 5:12-21 indicates that Paul thinks of faith in terms of obedience (p. 81).