Let's clarify something first because this question is tricky. 'Precious Is the Blood' isn't a book title. Joe Pace is a renowned gospel musician, and that phrase is the title of one of his most famous songs, often featured on live albums like 'Joe Pace Presents: The Celebration Choir.' So, if you're looking for a main message, you're in the realm of music and worship theology, not literature.
The core message of the song is a profound reflection on Christian atonement. It centers on the belief that the sacrificial blood of Jesus Christ is 'precious'—infinitely valuable and powerfully efficacious for redemption, cleansing from sin, and spiritual victory. The lyrics weave through themes of grace, deliverance, and reverence. It’s less a narrative with a plot and more a declarative, worshipful assertion of faith in that specific doctrine. The 'message' is essentially an exaltation of that cornerstone of belief, meant to inspire communal worship and personal conviction.
If you encountered this in a book context, it might be referenced in Christian devotional works or theological analyses of gospel music, but the primary source is the musical piece itself. The driving force is its emotional and spiritual intensity in a live worship setting, which a recording captures far better than text could.