Okay.
200 These are the words with which the Niceno-Constantinopolitan Creed begins. The confession of God’s oneness, which has its roots in the divine revelation of the Old Covenant, is inseparable from the profession of God’s existence and is equally fundamental. God is unique; there is only one God: "The Christian faith confesses that God is one in nature, substance and essence."3
234 The mystery of the Most Holy Trinity is the central mystery of Christian faith and life. It is the mystery of God in himself. It is therefore the source of all the other mysteries of faith, the light that enlightens them. It is the most fundamental and essential teaching in the “hierarchy of the truths of faith”.56 The whole history of salvation is identical with the history of the way and the means by which the one true God, Father, Son and Holy Spirit, reveals himself to men “and reconciles and unites with himself those who turn away from sin”.57
456 With the Nicene Creed, we answer by confessing: “For us men and for our salvation he came down from heaven; by the power of the Holy Spirit, he became incarnate of the Virgin Mary, and was made man.”
458 The Word became flesh so
that thus we might know God’s love: "In this the love of God was made manifest among us, that God sent his only Son into the world, so that we might live through him."72 "For God so loved the world that he gave his only Son, that whoever believes in him should not perish but have eternal life."73
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Taking up St. John’s expression, “The Word became flesh”,82 the Church calls “Incarnation” the fact that the Son of God assumed a human nature in order to accomplish our salvation in it. In a hymn cited by St. Paul, the Church sings the mystery of the Incarnation:
Have this mind among yourselves, which is yours in Christ Jesus, who, though he was in the form of God, did not count equality with God a thing to be grasped, but emptied himself, taking the form of a servant, being born in the likeness of men. And being found in human form he humbled himself and became obedient unto death, even death on a cross.83
Here are five key doctrines of the Catholic Church.