It is, in short, natural enough that Browning should have written his love letters obscurely, since he wrote his letters to his publisher and his solicitor obscurely.

In the case of Mrs.Browning it is somewhat more difficult to understand.

For she at least had, beyond all question, a quite simple and lucent vein of humour, which does not easily reconcile itself with this subtlety.

But she was partly under the influence of her own quality of passionate ingenuity or emotional wit of which we have already taken notice in dealing with her poems, and she was partly also no doubt under the influence of Browning.
Whatever was the reason, their correspondence was not of the sort which can be pursued very much by the outside public.

Their letters may be published a hundred times over, they still remain private.