In another article (195) we said that Catholicism and Evangelicalism were oil and water. This does not mean that we have to be unkind to each other; it does not mean we are to be uncivil with each other; it does not mean that we must live in the midst of each other without amicability. But one thing it does mean: we cannot worship God together.
Why does it mean that? Because there are two distinct and different Gods represented. This is not obvious at the verbal level. Both Catholicism and Protestantism claim the God of Jesus Christ as their God. But claims do not establish truth. Mormons claim to worship the God of Jesus Christ; Mohammedans claim to worship the God of Whom Jesus Christ was a prophet; and, in this century even Jews have begun to acknowledge Jesus as a great teacher of truth--indicating that even some Jews claim to be worshiping the God of Jesus Christ.
For a bit of historical perspective, consider Jesus' words in John 5:36-38 where He said that the religious leaders did not know His Father. Now, these were the religious leaders of His day in the chosen nation of God. They claimed to be worshiping the God of Abraham, Isaac, and Jacob. They claimed to be the disciples of Moses. They honored the written Word of God by intense study and extensive memorization. Yet, Jesus said that they were actually worshiping a different God than His Father.
So it is today. The Protestants own the God of Jesus Christ Who is characterized by the gospel of salvation by grace through faith alone. The Catholics own the God of Jesus Christ Who is characterized by the gospel of salvation by baptism and the pursuit of good works. There are two different gospels here and two different Gods.
Why can't the God be the same even though the gospels are different? Because God, the true One, is the God of Truth. He does not subscribe to any lie and any lying gospel does not represent Him.
It does no good to claim that Protestants and Catholics are in agreement in more areas than they are in disagreement. That was true of Jesus and those who crucified Him. They agreed on most of the major truths of Judaism with a major exception in one area: the message of how a man is justified before God. The same is true of most of the religious pluralism that exists in our world today. Most religions have many, many areas of agreement; but the gods are different because gods are not determined by broad areas of agreement, but by the critical area of disagreement on how a man is made right with God.
Is a man made right by faith? or is he made right by his performance? There can only be one correct answer; and only the correct answer points to the God of Truth. False answers point to false gods.
Catholicism and Protestantism are oil and water.