Catholicism advances Christ +Mary+Tradition + works.
The two aren't compatible.
Let’s put aside for the moment a discussion of whether this is a true representation or, if it is, the argument for one or the other..
Why does this hold us back from co-operating in spreading the Gospel?
Phrased differently:
Differences aside, how can we co-operate in spreading the Gospel?
Jesus Christ is Lord. That is the first and final affirmation that Christians make about all of reality. He is the One sent by God to be Lord and Savior of all: 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) Christians are people ahead of time, those who proclaim now what will one day be acknowledged by all, that Jesus Christ is Lord. (Philippians 2)What is holding us back from co-operating in spreading this Gospel?We affirm together that we are justified by grace through faith because of Christ. Living faith is active in love that is nothing less than the love of Christ, for we together say with Paul: I have been crucified with Christ; it is no longer I who live, but Christ who lives in me; and the life I now live in the flesh I live by faith in the Son of God, who loved me and gave himself for me. (Galatians 2)