The Person of Christ (Christology Proper)
Two whole, perfect, and distinct natures — Godhead and manhood — inseparably joined in one person, without conversion, composition, or confusion. WCF VIII.2 is the Standards' Chalcedonian statement. The Larger Catechism Q. 36-40 develops the incarnation and the personal union at length.
Westminster Confession
2 sections
The Son of God, the second person in the Trinity, being very and eternal God, of one substance, and equal with the Father, did, when the fulness of time was come, take upon him man's nature, with all the essential properties and common infirmities thereof, yet without sin: being conceived by the power of the Holy Ghost in the womb of the Virgin Mary, of her substance. So that two whole, perfect, and distinct natures, the Godhead and the manhood, were inseparably joined together in one person, without conversion, composition, or confusion. Which person is very God and very man, yet one Christ, the only mediator between God and man.
The Lord Jesus, in his human nature thus united to the divine, was sanctified and anointed with the Holy Spirit above measure; having in him all the treasures of wisdom and knowledge, in whom it pleased the Father that all fulness should dwell; to the end that, being holy, harmless, undefiled, and full of grace and truth, he might be thoroughly furnished to execute the office of a mediator and surety. Which office he took not unto himself, but was thereunto called by his Father, who put all power and judgment into his hand, and gave him commandment to execute the same.
Shorter Catechism
2 questions
The only Redeemer of God's elect is the Lord Jesus Christ, who, being the eternal Son of God, became man and so was, and continueth to be, God and man in two distinct natures, and one person, forever.
Christ, the Son of God, became man, by taking to himself a true body, and a reasonable soul, being conceived by the power of the Holy Ghost, in the womb of the virgin Mary, and born of her yet without sin.
Larger Catechism
5 questions
The only Mediator of the covenant of grace is the Lord Jesus Christ, who, being the eternal Son of God, of one substance and equal with the Father, in the fulness of time became man, and so was and continues to be God and man, in two entire distinct natures, and one person, forever.
Christ the Son of God became man, by taking to himself a true body, and a reasonable soul, being conceived by the power of the Holy Ghost in the womb of the virgin Mary, of her substance, and born of her, yet without sin.
It was requisite that the Mediator should be God, that he might sustain and keep the human nature from sinking under the infinite wrath of God, and the power of death; give worth and efficacy to his sufferings, obedience, and intercession; and to satisfy God's justice, procure his favor, purchase a peculiar people, give his Spirit to them, conquer all their enemies, and bring them to everlasting salvation.
It was requisite that the Mediator should be man, that he might advance our nature, perform obedience to the law, suffer and make intercession for us in our nature, have a fellow feeling of our infirmities; that we might receive the adoption of sons, and have comfort and access with boldness unto the throne of grace.
It was requisite that the Mediator, who was to reconcile God and man, should himself be both God and man, and this in one person, that the proper works of each nature might be accepted of God for us, and relied on by us, as the works of the whole person.