“With equal truth can it be affirmed that, by the will of God, nothing of the immense treasure of every grace which the Lord has accumulated, comes to us except through Mary . . . . How great are the wisdom and mercy revealed in this design of God . . . Mary is our glorious intermdiary; she is the powerful Mother of the omnipotent God . . . This design of such dear mercy realized by God in Mary and confirmed by the testament of Christ (John 19:26-27), was understood from the beginning and accepted with the utmost joy by the holy Apostles and the earliest believers. It was also the belief and teaching of the venerable Fathers of the Church. All the Christian peoples of every age accepted it unanimously . . . There is no other reason for this than a divine faith.” - Pope Leo XIII from his encyclical “Octobri mense”.
In connection with this remarkable passage we would like to make the following observations:
1.) The truth proposed by Pope Leo is: the will of God is that we obtain absolutely everything through Mary.
2.) The encyclical is addressed to the whole Church.
3.) The Pope appeals to the universal belief of the Church from the Apostles to our own day, thereby officially interpreting tradition. This unanimous consensus of the Ecclesia docens with the Ecclesia discens in a matter that could not be learned except through revelation is a guarantee that God did reveal it.
4.) Pope Leo gives us to understand that God implied this truth in the Annunciation pericope (Luke 1:26-38), and also in the proclamation of Christ from the cross, as narrated in St. John’s Gospel (19:26-27). Therefore, the doctrine is based on the written word of God.
Source: Armand J. Robichaud, S.M. - “Mary, Dispensatrix of All Graces”