At Christmas we celebrate the saving mystery of the Incarnation.
The Nativity of Christ is about the God who created the world becoming incarnate, while the foundations of the Earth are shaken. The Nativity of Christ is about Theosis, whereby we are deified, and by His grace, share in His Divinity, just as He has joined Himself with our humanity. (Abbot Tryphon, All-Merciful Savior Monastery)
God partook of our nature that we might partake of His nature by grace.
1 Simon Peter, a bondservant and apostle of Jesus Christ, to those who have obtained like precious faith with us by the righteousness of our God and Savior Jesus Christ: 2 Grace and peace be multiplied to you in the knowledge of God and of Jesus our Lord, 3 as His divine power has given to us all things that pertain to life and godliness, through the knowledge of Him who called us by glory and virtue, 4 by which have been given to us exceedingly great and precious promises, that through these you may be partakers of the divine nature, having escaped the corruption that is in the world… (2 Peter 1.1-4 NKJV)
God our Father,
our human nature is the wonderful work of your hands,
made still more wonderful by your work of redemption.
Your Son took to himself our manhood:
grant us a share in the godhead of Jesus Christ,
who lives and reigns with you in the unity of the Holy Spirit,
God for ever and ever. Amen. Source