At the moment Our Lady gave consent to the will of God proclaimed to her by the Angel Gabriel, God, the second person of the Blessed Trinity became man: “The Word became flesh.” This was the greatest moment in the history of the created universe. Our Lord was truly God and became truly man; therefore Our Lady conceived Him as a virgin, by the power of the Holy Spirit, not by means of the marriage act.
Our Lady was prepared for this vocation by God who preserved her, uniquely, from the stain of original sin. She remained sinless throughout her life and remained a virgin, cared for in marriage by St Joseph. Our Lord did not have siblings.
In our devotions, prayers and conversation, we must never forget that Jesus Christ is truly God. He came down to earth, born as a man like us in all things except sin. It is an error to think of Our Lord being “tempted” in the way that we are by spiritual weakness or past habits of sin. His suffering was increased by the perfect holiness of His humanity because He was acutely conscious of the damage done by sin to those whom He loves.
Sometimes people excuse laxity or compromise with Christian morality by saying “What would Jesus do?” This often means “What would I do if I were Jesus?” We are made to the image and likeness of God in Christ, but we prefer to re-make God into our own image and likeness, to make ourselves more comfortable with re-writing the Gospel. When we listen to the voice of the Saints, we encounter Christ in action, challenging us to be follow Him with full hearts and minds as Our loving and merciful Lord.