From The Guardian:
The picture of John Donne “in the pose of a melancholy lover”, which was recently bought by the National Portrait Gallery, has once again fixed a particular image of the poet in the public mind. He is soulful and amorous (the folded arms and sensual mouth), theatrical (the wide-brimmed black hat), dressy (the lacy collar and furred cuff), and enigmatic (the deep background shadows). And if that doesn’t sound intriguing enough, there’s more. An inscription bowed into a semi-circle round the top of the portrait reworks a phrase from a Latin psalm which can be translated as “O Lady lighten our darkness”. Does this mean the picture was originally intended for a lover, or is it a kind of prayer to the Virgin Mary, and therefore also a reference to Donne’s Catholic background? We can’t be sure. Like so much else about Donne, the inscription is ambiguous – as much a fusion of “contraries” as the man himself.
Donne was born in 1572, the son of Catholic parents who understood that if they wanted to get on in the world they would have to play down or actually disguise their faith.
More here.