In general, Chesterfield’s writings are utilitarian in nature and thus denude themselves of anything that would generate what constitutes true love. Still, from a practical standpoint his commentary in this case has a delightful ring.
Mostly because he did not provide for her (because she did not meet his standards) so she took all the letters Chesterfield had written to her husband, edited them and made them into a book that is still being read.
The son apparently disregarded his father's advice and married a nice intelligent woman who brought him no social advantages what so ever and had a happy life.