Rom 3:23 For all have sinned, and come short of the glory of God; The word all in the original language means "all, every, any". Rom 3:10 As it is written, There is none righteous, no, not one: Again the Greek word for none means "absolute negative or none". There are no exceptions in humanity- none. Mary calls God her Savior if she had no sin she would not need a Savior as only sinners need salvation: Luk 1:46 And Mary said, My soul doth magnify the Lord, Luk 1:47 And my spirit hath rejoiced in God my Saviour. That is specifically why God overshadowed or covered her: Luk 1:35 And the angel answered and said unto her, The Holy Ghost shall come upon thee, and the power of the Highest shall overshadow thee: therefore also that holy thing which shall be born of thee shall be called the Son of God. Jesus is God from before time. He made all that was, is or ever will be. Joh 1:1 In the beginning was the Word, and the Word was with God, and the Word was God. Joh 1:2 The same was in the beginning with God. Joh 1:3 All things were made by him; and without him was not any thing made that was made. Jesus came to pay the price for our sins. He needed an human body to do so. This human body came from a quite human girl named Mary. She gave him His fleshly body but He existed before anything else.