"Christ, because He was conceived by…Spirit-ual power, is called ‘the Holy Seed’…. Though Christ was formed of the seed of Abraham, yet He contracted no defilement from a sinful nature. For the Spirit of God kept Him pure from the very commencement.
:And this was done not merely so that He might abound in personal holiness, but chiefly so that He might sanctify His Own people." Indeed, even from their conception onward (First Corinthians 7:14).
As the Calvinistic Westminster Confession (8:2f) observes: "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…yet without sin, being conceived by the power of the Holy Ghost. Luke 1:35."