In Luke’s Gospel, Mary is told that she is “blessed among women” by Elizabeth, under the power of the Holy Spirit. Some manuscripts of Luke also report the angel Gabriel saying the same thing when he greets Mary to report that she has been chosen to be the mother of the Son of God. Whether this belongs or not, we know that the statement is true, for there is no question regarding Elizabeth’s inspired shout.
Now the phrase ‘blessed art thou’ connotes, to our English ears, only that Mary is blessed - but to Aramaic ears, it connotes a great deal more. Mary would have spoken Aramaic, as did most non-dispersed Jews at the time, which is a Semitic language. Semitic languages have all sorts of interesting characteristics, but the one that is of interest to us now is that there was no word in them for ‘most,’ ‘least,’ ‘more,’ ‘less,’ or any other terms of degree.
To say these things, Aramaic speakers used expressions and forms of speech. If an Aramaic speaker wanted to say that you were smarter than him, he would say, “You are smart to me,” or something similar. To say in Aramaic that a person is the smartest person in the room, one would say “you are smart among them,” or something similar. These are only examples, but hopefully it conveys the point. Given this fact, when Elizabeth, inspired by the Holy Spirit, says “blessed art thou among women,” she is simply saying, in the manner her language required, that Mary is the most blessed of all women. It is a very strong statement. (Note that while it is true that Luke was written in Greek, it recorded Aramaic-speaking people and therefore would have included their idioms, as is made clear by other Semitic idioms that are found throughout.)
The implications of this are staggering. If Mary is most blessed of all women, she must be more blessed then Eve. Eve was blessed in several ways, but one important way was that she was born without Original Sin - born with Grace, in a right relationship with God. However, Eve fell into sin; she lost that grace. The only way it could be said that Mary was more blessed than Eve would be if Mary was not only born in Grace, which would make her as blessed as Eve, but that she also never fell into sin in the first place – that she never sinned. From this we get two important truths: first, that Mary was conceived without original sin just as Eve was, and second, that Mary never lost the Grace in which she was made through sin, and thus never sinned in her entire life. The most blessed anyone could be would be to have God's Grace and to be free of a fallen nature, for then one could follow God perfectly in every way. Eve had this and so she was the most blessed woman ever - nobody else had this incredible blessing of being able to perfectly obey and love God. Mary then came into the world and, by not only having but maintaining this blessing for all of time and eternity, became more blessed than Eve, fulfilling Elizabeth’s inspired words.
Of course, there are several counter-arguments that some may raise against this, but some thought will show why it truly is such powerful statement. The biggest blessing one can possibly receive is God's grace and to be completely in line with what God wants of us. Everything else, especially material and emotional goods, even being able to carry God in one’s womb, pales in comparison to being perfectly in line with God, being without original sin, and without its consequences. A woman could carry God Himself in her womb and still go to Hell because of her fallen nature, her ability to reject God’s salvation, or the possibility that she may never accept it in the first place. Thus, arguments to the effect that Mary’s blessedness lay in the great privilege of bearing Christ fall far short.
It is important to realize that this is all by the Grace of God – not by any doing of Mary’s. All people need God's grace. Without grace, we would not even be here right now. Without the free gift of God keeping us in existence, we would simply cease to exist. Even more than that, we are all creatures and do not deserve to see God in Heaven. The very ability to go to Heaven at all is Grace. As was mentioned above, Adam and Eve were created in and by Grace. They had it from the first moment of their existence. It was not simply natural to them to be in God's good favor. It was not natural to them to be able to dwell with God in the garden. That was all grace, even though they had not yet sinned. Mary certainly needed God's Grace, and the Catholic Church teaches this. She was born immaculate because of It. It was Christ's death on the cross that earned for Mary the Grace of being conceived without Original Sin. His sacrifice on the cross was applied to her at the moment of conception even though it hadn't yet happened, because God is outside of time. Christ's death also saved Moses and Abraham and other Old Testament people before it had actually happened because God can apply the Grace Christ earned early by virtue of His being outside of time.
So then Mary did need a saviour, she did need Christ's Grace, and the only reason she was conceived immaculate was because of it.