John Piper echoing Martyn Lloyd-Jones

There is a popular quote from Martyn Lloyd-Jones which I hear cited more than any other. In commenting on Paul's words in Romans 6:1, where he quotes his opponents as saying:

What shall we say then? Are we to continue in sin that grace may abound?

Lloyd-Jones famously said:

The true preaching of the gospel of salvation by grace alone always leads to the possibility of [the charge that we may sin that grace may abound] being brought against it. That is a very good test of gospel preaching....
If my preaching and presentation of the gospel does not expose it to that misunderstanding, then it is not the gospel....If your preaching of salvation has not been misunderstood in this way, then you had better examine your sermons again,
and you had better make sure that you are really preaching the salvation that is offered in the New Testament to the ungodly, to the sinner, to those who are dead in trespasses and sins, to those who are enemies of God.

And John Piper, in commending Doug Wilson, forthcoming Desiring God conference speaker, says that

If you don't preach in such a way that somebody responds like Romans 6:1, you're probably not preaching the gospel.