In Pride and Prejudice Chapter 13:
As a clergyman, moreover, I feel it my duty to promote and establish the blessing of peace in all families within the reach of my influence; and on these grounds I flatter myself that my present overtures are highly commendable, and that the circumstance of my being next in the entail of Longbourn estate will be kindly overlooked on your side, and not lead you to reject the offered olive-branch. I cannot be otherwise than concerned at being the means of injuring your amiable daughters, and beg leave to apologise for it, as well as to assure you of my readiness to make them every possible amends—but of this hereafter.
What does "but of this hereafter" mean? I don't understand the usage of "but of" here.