Matthew 1:18 says, 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.  Maybe I should have waited to closer to when we celebrate Christmas to look at the birth of Christ, but we need to remember His birth all year, and not just on a particular day.  This verse tells us of the miracle of the conception of Jesus and a fulfillment of a promise of God.  Jesus, the Messiah, would be born of a virgin.  Mary was espoused to Joseph, which was more like a an even greater commitment than we have with an engagement, I believe.  Mary was expecting a child, but Joseph and she had not been together in a sexual relationship.  Verse nineteen states, Then Joseph her husband, being a just man, and not willing to make her a publick example, was minded to put her away privily.  This verse refers to Joseph as an honorable man who did not want to bring dishonor to Mary, but he had to have believed that she brought dishonor to him.  He was seeing only with a physical understanding and not a spiritual one.  Verse twenty says, But while he thought on these things, behold, the angel of the Lord appeared unto him in a dream, saying, Joseph, thou son of David, fear not to take unto thee Mary thy wife: for that which is conceived in her is of the Holy Ghost.  God did not leave Joseph to his own understanding, but sent an angel to present the truth of Mary's pregnancy to him.  Mary was pregnant by the Holy Spirit.  We may not be able to really understand how this was achieved, but we can be certain that it did.  The God Who created all can certainly create one miraculous baby.  Jesus' physical life did not begin at birth, but at conception, as I believe all life does.  Verse twenty-one says, And she shall bring forth a son, and thou shalt call his name JESUS: for he shall save his people from their sins.  This was way before ultrasound, but Joseph was told by the angel that Mary was going to have a Son.  Joseph was also told that he was to name the baby Jesus, for He would save his people from their sins.  It is hard to imagine how difficult it must have been for Joseph to accept this.  The only way to do so would have been by faith in God.  Verse twenty-two says, Now all this was done, that it might be fulfilled which was spoken of the Lord by the prophet, saying,  The birth of Jesus, the Messiah, had been foretold by prophets of old, and that prophecy was now being fulfilled.  Verse twenty-three states, Behold, a virgin shall be with child, and shall bring forth a son, and they shall call his name Emmanuel, which being interpreted is, God with us.  This prophecy that was referred to is found in Isaiah 7:14.  Verse twenty-four declares,  Then Joseph being raised from sleep did as the angel of the Lord had bidden him, and took unto him his wife:  Joseph could have just thought that he had a weird dream, but he put his faith in God's revelation into action.  It is not enough to just know what God wants us to do, but we must act on that knowledge.  Verse twenty-five says, And knew her not till she had brought forth her firstborn son: and he called his name JESUS.  Joseph married Mary, and did not have a sexual relationship with her until after the birth of Jesus.  I believe that only his faith in God allowed him to do this.  If God calls us to do anything, by our faith in Him we will be able to do it.