Penal substitution explained by John Piper

My hero John Piper has made his book defending the classical view of the atonement available for free online. I shall no doubt blog through that book. The blurb says

“Does Christ’s life-long record of perfect obedience to God get ‘credited’ to your account when you trust in Christ and are ‘justified’ by God? This has been the historic Protestant understanding of the ‘imputation of Christ’s righteousness,’ but John Piper warns that we are in danger of losing this doctrine today, because of attacks by scholars within the evangelical camp. In response, Piper shows, in careful treatment of passage after passage, that the imputation of Christ’s righteousness to believers is clearly the teaching of the Bible, and if we abandon this doctrine we will also lose justification by faith alone. I am thankful to God for John Piper’s defense of this crucial doctrine.”