Grace Essentials, by J.C. Ryle
I've read appreciatively from Ryle over the years, particularly in Holiness and Thoughts for Young Men. Having profited from these, I was pleased with the invitation to home in on this book for purposes of commendation.
In my experience, devotional books often require that you approach them with an elevated frame of mind to receive their blessing, but Grace Essentials does the heavy lifting for you. Whether you come to it cranky or weary or worldly in spirit, it takes charge (with Ryle's plain-spoken, no-nonsense, bracing-yet-amiable, Spirit-filled, winsomely-reasonable, thematic treatments of Scripture) and sets you afresh on your Christian walk. His 19th-century words have 21st-century accessibility and power, whether for evangelism or edification.