Whenever our Blessed Mother is referred to as a co-redemptrix or mediatrix, some people object and quote 1 Tim 2:5 that says Jesus is the one mediator. But in 1 Cor. 9:22, St. Paul says he became all things to all people so that he might save some. Not being the Redeemer, how could he do that? In 1 Tim 4:16, St. Paul encourages Timothy to adhere to his teaching so that he (Timothy) might save others as well as himself. Huh? What about the one mediator? To see how these statements are not contradictory and to be able to answer the objections some may have, it’s important to understand the difference between an efficient cause and an instrumental cause.
An efficient cause is the source of an action, without which there can be no effect. If you choose not to write a letter, it won’t get written. An instrumental cause is one that assists the efficient cause in bringing about an effect. When you decide to write your letter, a pencil could be an instrumental cause to assist you. So could a pen or a computer, or any other means that helps you, the efficient cause, to get it written. Now apply this to salvation.
First of all and most importantly, Jesus truly is the only Redeemer, thus making Him the one mediator between God and man. That also makes Him the efficient or principal cause of all things, for without Him we can do nothing (John 15:5). We, however, become instrumental causes when we act on His behalf. Although Jesus is the efficient cause and source of our salvation and without Him no one is saved, any one of us can participate as an instrumental cause by praying, teaching God’s Word, giving proper example, etc. God’s graces help us, His “instruments”, to act in this regard. Per Paul and Barnabas (Acts 13:47): For so the Lord commanded us, "I have made you a light to the Gentiles, that you may be an instrument of salvation to the ends of the earth."
St. Paul never implies that he is the source or direct cause of anyone’s salvation, and in fact he says just the opposite (1 Cor. 3:5-9). Neither do we imply this when we acknowledge the special role of our Blessed Mother. Rather, we recognize the potential for someone to be a co-worker and instrument of God to effect another’s salvation. All of us have that same potential simply by knowing and living the apostolic faith taught by the guidance of the Holy Spirit in and through the Catholic Church.