In a letter to Thomas Wipf in Zurich on October 31, 1963, Karl Barth wrote from Basel a helpful summary of the points of disagreements between Roman Catholics and Protestants. Karl Barth had many Roman Catholic friends, such as Hans Küng whom was a principle character at Vatican II. These seven concise points are a helpful list of Protestant protests, and the two appended warnings are also important to consider in each of these seven points:
#126 To Thomas Wipf, Zurich
Basel, 31 October 1963
Dear Mr. Wipf,
Your letter of 11 Oct. has gone unanswered for too long.
The present situation (the council [Vatican II] and the inner movements behind it) is a warning that we must state the differences carefully. Are there really irreconcilable antitheses? Or are there differences only in emphasis?
Evangelical: Unconditional precedence of God's free grace over against the "good" being and action of men (even Christians).
Roman Catholic: Tendency to reverse this relation.
Ev.: The Bible has strictly the first word over against church tradition.
R.C.: Tendency to understand the Bible in the light of tradition instead of the opposite.
Ev.: The church is God's people within which are certain ministering functions ("offices").
R.C.: Inclination to regard these as a priestly hierarchy around which the people (the "laity") must gather.
Ev.: The church's unity rests on God's living Word (in Jesus Christ through the Holy Spirit), and only incidentally on legal ordinances.
R.C.: Inclination to understand spiritual order in terms of a legal order.
Ev.: Central significance of proclaiming (preaching) the biblical gospel.
R.C.: Prevailing concentration on administering the so-called "sacraments."
Ev.: Respect and gratitude for the existence of good examples of the Christian life.
R.C.: Veneration and invocation of the "saints."
Ev.: Centrality of Jesus Christ as true Son of God and Man.
R.C.: Apparent sharing of this centrality by Mary as the human mother of God.
Here are seven points where you may safely proceed so long as you are careful. Care is required for two reasons:
1. because many things are fluid in modern Roman Catholicism and may lead to agreements and then to modifications of the total picture;
2. because we Evangelicals for our part are not on top of our own cause and must look out lest the first might become last and the last first.
With friendly greetings and all good wishes for your project on 22 Nov,
 Wipf had asked Barth for help in making a report on the main differences between the Roman Catholic and Protestant confessions.
Karl Barth, trans. Geoffrey Bromily, Karl Barth Letters: 1961-1968, #126 Second Edition, pages 137-138.