A Play on Words
I just wanted to add that Donne's poem below has a subtle and very personal meaning.
Donne's lines:
When thou hast done, thou hast not done
is a play on the verb "to do" and Donne himself. God still has not Donne's, the poet's, renunciation and abstinence from sin, and thus has not done, accomplished His task.
Finally, through Christ, as in the lines
that at my death thy Son
Shall shine as he shines now, and heretofore;
And, having done that, thou hast done;
God finally has done his task, and also has Donne.