Nothing except the Resurrection of Jesus Christ is a greater miracle or wonder in human history. God becoming flesh in human history is the greatest marvel. Avatar is what this is called in Hindu religious tradition. Jesus of Nazareth was foretold in the Torah and the Prophets centuries before his appearance and he was proved to be real and not a pretender due to his death and Resurrection. The early church grappled with all of this intellectually. Many heresies were confronted, answered, and dismissed. Throughout the 2000 plus years of church history, many of the early church heresies have reappeared over and over again. Whether you are Catholic or Protestant the answers are from the Word of God.
On the Incarnation of the Word of God is a classic theological treatise written by Athanasius, Bishop of Alexandria, the early church father often called the "Father of Orthodoxy". Athanasius defends the doctrine that Jesus Christ is both God and Man and shows the necessity of Christ's Incarnation, Death, and Resurrection.