Catholics do not believe that there is any other mediator of redemption than our Savior Jesus Christ, “And there is salvation in no one else, for there is no other name under heaven given among men by which we must be saved” (Acts 4:12). When we call the Blessed Mother or any other saint a mediator it is not in the sense of the mediator of the redemption attributed to our Savior, but in the sense of an intercessor or pleader, in which sense any Christian may be called a mediator. This mediatorship is the same as when Abraham, or Moses, or St. Paul interceded or mediated between God and man. We are mediators whenever we pray for a friend, relative, or neighbor. God himself commanded Eliphaz and his friends to ask Job to pray for them, and God promised to accept his prayers.
Job 42:8-9 – “After the LORD had spoken these words to Job, the LORD said to Eliphaz the Temanite: “My wrath is kindled against you and against your two friends; for you have not spoken of me what is right, as my servant Job has. 8 Now therefore take seven bulls and seven rams, and go to my servant Job, and offer up for yourselves a burnt offering; and my servant Job shall pray for you, for I will accept his prayer not to deal with you according to your folly; for you have not spoken of me what is right, as my servant Job has”.
In this sense, Moses could also say: Dt. 5:5 – “While I stood between the LORD and you at that time, to declare to you the word of the LORD; for you were afraid because of the fire, and you did not go up into the mountain”.