Sinless from the point of conception through all of eternity. The door through which the Son of God came to Earth as a man. Chosen by The Father from all eternity to bear His only begotten son. 

And so we pray, with Blessed Teresa of Calcutta:

“Mary, give me your Heart: so beautiful, so pure, so immaculate; your Heart so full of love and humility that I may be able to receive Jesus in the Bread of Life and love Him as you love Him and serve Him in the distressing guise of the poor.”

See more at Aletia.org

We do not consecrate ourselves to Mary’s heart, but through it

And here’s a good overview of some of the biblical reasons we honor – not worship – Mary…