If you're a Catholic Christian and want to appreciate your faith more, these books will serve you well. If you're not Catholic or Christian and wish to encounter the most persuasive apologetics, this is an excellent place to start.
Chesterton is a wonderful writer. A poet by nature, Chesterton focuses on the material and concrete in ways that seems both paradoxical and wondrous. In "Saint Francis of Assisi," Chesterton takes the most popular saint, and presents all those details that really make us modern secularists most uncomfortable with him. In another book here, he links St. Thomas Aquinas to Francis, showing that, despite their vast differences in temperament, they both strove to save and present the goodness of creation and nature and to rebuke (in word or action) those who would hold the bodily in disdain.
In a sense, the biographies here are more than biographies. They're filled with diversions, and those diversions all point in the direction of the remaining book, "The Everlasting Man," which is presented between the other two. The central point here is that the Incarnation is the central event of human history; it allows us to joyously celebrate the good of creation and nature, as God has blessed matter with His very being.
Also, Chesterton is a real pleasure to read, as this passage shows: "One of my first journalistic adventures, or misadventures, concerned a comment on Grant Allen, who had written a book about the Evolution of the Idea of God. I happened to remark that it would be much more interesting if God wrote a book about the evolution of the idea of Grant Allen."
His wit shines in the conclusion of this anecdote. To his bemusement, his editor castigates *him* for being blasphemous. "In that hour I learned many things, including the fact that there is something purely acoustic in much of that agnostic sort of reverence. The editor had not seen the point, because in the title of the book the long word came at the beginning and the short word at the end; whereas in my comments the short word came at the beginning and gave him a sort of shock. I have noticed that if you put a word like God into the same sentence with a word like dog, these abrupt and angular words affect people like pistol-shots. Whether you say that God made the dog or the dog made God does not seem to matter; that is only one of the sterile disputations of the too subtle theologians. But so long as you begin with a long word like evolution the rest will roll harmlessly past; very probably the editor had not read the whole of the title, for it is rather a long title and he was rather a busy man."