The context changes nothing about what is said here:
"Since faith is the foundation, the source, of the gifts of God by which man is raised above the order of nature and is endowed with the dispositions requisite for life eternal, we are in justice bound to recognize the hidden influence of Mary in obtaining the gift of faith and its salutary cultivation - of Mary who brought the "author of faith" into this world and who, because of her own great faith, was called 'blessed.' 'O Virgin most holy, none abounds in the knowledge of God except through thee; none, O Mother of God, attains salvation except through thee; none receives a gift from the throne of mercy except through thee" (ADIUTRICEM (On the Rosary), Encyclical of Pope Leo XIII, promulgated on September 5, 1895).
Here we see that Rome teaches that no one can have the knowledge of God EXCEPT THROUGH HER.
Since it is by "faith" that a person comes to the knowledge of God then Rome is teaching that no one can have faith except through Mary and hence no one can be saved except through her. That is why we read:
"None, O Mother of God, attains salvation except through thee."
That idea is directly contradicted by what Peter said here:
"Be it known unto you all, and to all the people of Israel, that by the name of Jesus Christ of Nazareth, whom ye crucified, whom God raised from the dead, even by him doth this man stand here before you whole. This is the stone which was set at nought of you builders, which is become the head of the corner. Neither is there salvation in any other: for there is none other name under heaven given among men, whereby we must be saved" (Acts 4:10-12).