This is a lesson about the mystery of the Holy Trinity. It explains the concept of "mystery" in theology, asserting that while these truths surpass human understanding, they are not unknowable. The lesson emphasizes the importance of the Holy Trinity as the central mystery of Christian faith and life, revealing its significance in both the history of salvation and the truths of faith. It explores the Trinity's representation in the Bible and how it is articulated in teachings, particularly in the Catechism of the Catholic Church.