“Therefore the Word of God, Himself God, the Son of God became man”

St. Simon of Cyrene Orthodox Mission (about)
 
“Therefore the Word of God, Himself God, the Son of God who “in the beginning was with God,” through whom “all things were made” and “without” whom “was nothing made” (John 1.1-3), with the purpose of delivering man from eternal death, became man: so bending Himself to take on Him our humility without decrease in His own majesty, that remaining what He was and assuming what He was not, He might unite the true form of a slave to that form in which He is equal to God the Father, and join both natures together by such a compact that the lower should not be swallowed up in its exaltation nor the higher impaired by its new associate. 
Without detriment therefore to the properties of either substance which then came together in one person, majesty took on humility, strength weakness, eternity mortality: and for the paying off of the debt, belonging to our condition, inviolable nature was united with possible nature, and true God and true man were combined to form one Lord, so that, as suited the needs of our case, one and the same Mediator between God and men, the Man Christ Jesus, could both die with the one and rise again with the other.” 

St. Leo the Great (5th century).

See also

Dear Santa, please grow up and become St. Nicholas! (from The Modern Monastic Order Of Saint Simon of Cyrene)