Matthew Poole and continuators on Matthew 1:18

18 Now the Birth of Jesus Christ was on this wise, when as his mother Mary was espoused, to Joseph, before they came together, she was found with child of the holy Ghost.

The Evangelist prefaceth this extraordinary Birth of our Saviour in this manner. Now, the Birth of Iesus Christ was on this wise, not in the ordinary Course and manner in which Children are conceived and brought forth into the World, but in this wonderful manner [when his mother Mary was espoused to Ioseph.] Betrothing, or Espousing, was nothing else but a Solemn promise of Marriage made by two Persons each to other, at such distance of time, as they agreed upon. It was a Decent usage approved of (if not ordained) by God, as appears by Deut. 20.7. That we are obliged still to use it, I dare not say, it might be a prudential Order and Constitution of that State. There was nothing in it Typical, nothing to bring it under the Notion of a Carnal Ordinance, (as the Apostle calls some of their Ordinances relating to the Worship of God) It seemeth Equitable, that the Parties to be Married might have some Convenient time to think seriously of the great Change they are soon to make in their Lives, and more solemnly seek unto God for his Blessing upon them, as also that they might more freely Discourse together about their Houshold Affairs, and the Settlement of their Families, then the modesty of the Virgins of that age would otherwise have allowed them. It made them Man and Wife before God, tho they came not together for some time after: The distance of time, seemeth to have been left to the Agreement of Parties, and Parents. In this Case we cannot certainly assert the distance, but it appeareth to have been such, as that she was found with Child, before they came together. Mary knew what the Evangelist here asserteth, that it was by the Holy Ghost: For as she must know, that she had not known Man, as she told the Angel, Luk. 1.34. So the Angel had satisfied her, saying, v. 35. The Holy Ghost shall come upon thee, and the Power of the most high shall overshadow thee. Therefore also that Holy thing which shall be born of thee, shall be called the Son of God. It cannot be doubted but that she revealed this to some of her Friends, but how it came to be found, or who found it we are not told. Ioseph as yet had no such Revelation. God would have his Son to be born of a Virgin. 1. For the fulfilling of the Promise, Isa. 7.14.2. Of the Holy Ghost, that the Womb of the Virgin being sanctified by the Spirit of Holiness, there might be no Traduction of Original sin. Of a betrothed Virgin. 1. That he might not be under the Reproach of Illegitimacy. 2. Nor his Mother subjected to the Punishment of the Judaical Law. 3. That Maries stock might be by her betrothed Husband. 4. That Christ might have a Guard in his Infancy.

Marginal references: Luk. 1.27.