The incarnation of the Son of God.
“We confess, therefore, that God has fulfilled the promise He made to the fathers by the mouth of His holy prophets1 when, at the time appointed by Him,2 He sent into the world His own only-begotten and eternal Son, who took the form of a servant and was born in the likeness of men (Php 2:7). He truly assumed a real human nature with all its infirmities,3 without sin,4 for He was conceived in the womb of the blessed virgin Mary by the power of the Holy Spirit and not by the act of a man.5 He not only assumed human nature as to the body, but also a true human soul, in order that He might be a real man. For since the soul was lost as well as the body, it was necessary that He should assume both to save both.
Contrary to the heresy of the Anabaptists, who deny that Christ assumed human flesh of His mother, we therefore confess that Christ partook of the flesh and blood of the children (Heb 2:14). He is a fruit of the loins of David (Acts 2:30); born of the seed of David according to the flesh (Rom 1:3); a fruit of the womb of the virgin Mary (Lk 1:42); born of woman (Gal 4:4); a branch of David (Jer 33:15); a shoot from the stump of Jesse (Is 11:1); sprung from the tribe of Judah (Heb 7:14); descended from the Jews according to the flesh (Rom 9:5); of the seed of Abraham,6 since the Son was concerned with the descendants of Abraham. Therefore He had to be made like His brethren in every respect, yet without sin (Heb 2:16-17, 4:15).
In this way He is in truth our Immanuel, that is, “God with us” (Mt 1:23).”
-Belgic Confession (1561), Article 18, The Incarnation of the Son of God