I love little children. They bring so sweet a light to the world. Every child has a pure and undefiled spirit. Even though I love all children, I can easily admit that my own children bring me greater joy than all the other the children in the world. No child is as cute as mine, as smart as mine, as fun to be with as mine, and I care for no other children more than my own.
I believe that we are all children of our Heavenly Father who loves us, perfectly, and infinitely. Yet there was one among the spirit children of God, the firstborn of the Father, who was loved with more love than the rest of us if that is possible for God. If God loved us all the same than perhaps the distinguishing feature of Jesus was that he loved Heavenly Father the most. This righteous and perfect son was also the only spirit child of God who received his physical body with God as the parent. This is why we say that Jesus is the Only Begotten of the Father.
His mortal mother Mary carried this divine child and thus Jesus became the only one capable of completing the Atonement, having within him the blood of divinity that could be shed forever, and the blood of mortals that allowed him to feel every pain we have endured.
This genetic masterpiece gave way to the being who is full of grace and thus the perfect candidate for a redeemer. He was and is holy because he was the Only Begotten Son of the Man of Holiness.