What's the response?

[E]ven in the New Testament, there appears to be a sin that is beyond prayer for forgiveness. The challenge for the intercessor is to exercise spiritual discernment like Amos, to know when and how long one is to persist in intercession for a particular person or situation. Seeing a brother or sister committing sin, should not lead automatically to a judgmental attitude but, like Amos, to prayer.—Standing in the Breach, pages 503–4

<idle musing>
Not sure how much I agree with the first part, although 1 John does seem to imply what he's saying. But, I can definitely get behind the second half: prayer should always be our first response, although I sadly confess it isn't always. When we hear of, see, or experience firsthand a person sinning, or first response should be an involuntary one similar to Amos's: "Lord, forbear, Israel is so small!"
</idle musing>