In our day of religious pluralism, there is a tendency among Christians to be more inclusive than Christ. Who are Christ's people? Those who have repented from their sin and turned to Christ for the forgiveness of sin based upon his work on the cross. These have been baptized; therefore, they are members of the Church.
Should we be inclusive of Roman Catholics into the Church? There are two responses to this question: first, institutionally the Reformers of the 16th century declared convincingly that Rome is apostate. It has modified the gospel of grace and faith and turn it into one of grace, faith, and works to maintain justifying grace. Roman Catholics readings this may cry foul! It's okay. Second, I believe that there are members of Roman Catholic churches who are part of the Church; yes, they have repented from sin and have trusted in Christ alone for their salvation.
In 1545-1563, the Council of Trent (an ecumenical council of the Roman Catholic Church) declared that those who believe in justification by faith alone, or those who believe in two sacraments are anathema---accursed. The Canons of Trent are still operative and binding and dogmatic. How can Anglicans, Lutherans, Presbyterians, and Reformed speak of rapproachment with Rome when Rome has never retracted those anathemas against Protestants laid it in the Canons of Trent?
This is a gospel issue, not merely an intramural disagreement. Luther stated that the doctrine of justification of faith alone is the article by which the Church stands or falls. He was right. If a Church denies this doctrine, is it still a Church? No. Let us heed Paul's inspired declaration rather than Trent's: "But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed." Compare the gospel revealed in the inspired Scriptures to what Rome promotes as the gospel. You will find that Rome, not historic Protestantism, is accursed.
I write this to help we who claim to be Protestant to preach the gospel clearly and with love, but also to encourage us to pray for Roman Catholics we know; let us pray that God would be pleased to gather his own from the ranks of that apostate church. Lord, have mercy!