David Herbert Donald is a two time Pulitzer Prize winning historian highly respected in the Lincoln scholarship community. His most famous book is simply called "Lincoln," and is a must-read for everyone interested in our 16th President.
This book, "Lincoln at Home," is a thin volume giving "two glimpses" of Abraham Lincoln's family life. And glimpses are what they are. The first is based on a lecture Donald gave at the White House in 1990 at the invitation of then President George H.W. Bush. In it Donald gives superficial insights into the Lincoln family life. The information is delightful, though not particularly deep.
The second glimpse is reproduction of the extant letters between Lincoln and Mary and their eldest son Robert. The earliest letter occurs during Lincoln's one term as U.S. Congressman in 1848, from him to Mary while she was visiting with relatives in Kentucky. Many of the "letters" are actually telegraph messages during the Civil War as Mary traveled to New York and other points north to get away from the strain of the war. These telegraph messages are by necessity shorter and less intimate than the actual letters.
Overall the book is an interesting and quick to read view - glimpse is the correct word here - of their relationship. As such it barely scratches the surface. Very few letters and other correspondence remains between the couple, perhaps because Robert took control of all Lincoln's papers after his assassination and reportedly burned much of the private correspondence. The glimpses in this book are a nice introduction for those with little background on the pair, but anyone wishing to get a deeper analysis should read one of the full-length biographies, in particular those that focus on Mary and the marriage (e.g., by Jean Baker, Catherine Clinton, Daniel Mark Epstein, and Mary's niece, Katherine Helm).