These four essays of Ambrose, the forceful and scholarly Bishop of Milan and the metropolitan of the churches of northern Italy in the late fourth century, expound upon both sacramental and Trinitarian theology. The two essays on "the mysteries" and on "the sacraments" provide a window into the liturgical practices of the ancient Italian church, for which Ambrose-ever the Scripture scholar par excellence-explains the biblical basis. Two other essays, one a response to Arianism and the other a refutation of the contentions of those who opposed the full divinity of the Holy Spirit, together constitute a robust defense of the doctrine of the Trinity, influenced by Greek Christian theological writings and grounded on Scripture.