When is a gospel not a gospel?

This question, when asked in earnest, is wonderfully clarifying. F. F. Bruce answered it this way:

To sum up, then, we may say that, according to the general consensus of New Testament teaching, a gospel is not a gospel when—

1. it is detached from the Jesus of history;
2. it gives little or no place to the passion;
3. it exalts human achievement in place of the grace of God;
4. it adds other conditions to the one which God has declared acceptable (even if those additions be things good and desir­able in themselves);
5. it treats righteousness and purity as things which the truly spiritual man has outstripped.
   

On the other hand, a gospel is a gospel when—

1. it maintains contact with the Jesus of history, affirming that this same Jesus who came in the flesh and died is the vindicated and exalted Lord;
2. it embraces and proclaims “the stumbling-block of the cross”;
3. it extends the grace of God to men for their acceptance by faith;
4. it relies upon the power of the Spirit to make it effective in those who hear it;
   
5. it issues in a life of righteousness and purity which is sustained and directed by the love of God.

I lifted this whole from a post at BiblicalStudies.org.uk, which I discovered through the services of Milton Stanley, who through his many helpful links is always helping me to see and think clearly about matters of first importance.