The book covers 590-1073 (from Pope Gregory I to Pope Gregory VII) and deals with the development of theology, church life, the church state relationship, and the decline of the church into legalism, superstition, and idolatry, along with the heroic resitance of faithful Christians to that decline. The rise of Islam also is dealt with in this volume, and includes an interesting footnote by Schaff on "the Mormon question."
I think one of the best parts of the volume was Schaff's analysis of Medieval poetry and hymns, including the question/answer poem Art thou weary by Stephen the Sabaite:
Art thou weary, art thou languid,
Art thou sore distrest?
'Come to me'- saith One- 'and coming
Be at rest!'
Hath He marks to lead me to Him
If He be my Guide?
'In His feet and hands are wound-prints,
And His side.'
Is there diadem, as Monarch,
That His brow adorns?
'Yea, a crown in very surety,
But of Thorns!'
if I find Him, if I follow,
What His guerdon here?
'Many a sorrow, many a labor,
Many a tear.'
If I still hold closely to Him,
What hath He at last?
'Sorrow vanquished, labor ended,
If I ask Him to receive me,
Will He say me nay?
'Not till earth, and not till heaven
Finiding, following, keeping, struggling,
Is He sure to bless?
'Angels, martyrs, prophets, virgins,
eBook History of the Christian Church