Saint Augustine of Hippo - Confessions (Pusey translation)

The Confessions outlines Augustine's sinful youth and his conversion to Christianity. It is widely seen as the first Western autobiography ever written, and was an influential model for Christian writers throughout the following 1,000 years, through the Middle Ages. It is not a complete autobiography, as it was written in his early 40s, and he lived long afterwards, producing another important work (City of God). It does, nonetheless, provide an unbroken record of his development of thought and is the most complete record of any single person from the 4th and 5th centuries. It is a significant theological work, featuring spiritual meditations and insights. It begins:

"GREAT art Thou, O Lord, and greatly to be praised; great is Thy power, and Thy wisdom infinite. And Thee would man praise; man, but a particle of Thy creation; man, that bears about him his mortality, the witness of his sin, the witness, that ]Thou, O God, resistest the proud: yet would man praise Thee; he, but a particle of Thy creation. Thou awakes us to delight in Thy praise; for Thou madest us for Thyself, and our heart is restless, unless it repose in Thee.”

(Summary from Wikipedia and Book I, Chapter I.)