So the reunion must be on Catholic grounds. That is, complete, universal grounds. That is the essentially and distinctively Catholic point: essential Catholic point and it is non-negotiable for any faithful Catholic.
But at the same time, reunion must be on Protestant grounds. And these are equally non-negotiable. What I mean by that is the essentially and distinctively Protestant point: the central Protestant point seems to be the opposite of the Catholic one, namely the simple all sufficiency of Christ alone. Jesus only. Jesus plus nothing. Jesus straight, not mixed drink. If reunion is possible, that is its only foundation. The Church’s one foundation is Jesus Christ her Lord.
Now of course that doesn’t have to mean, and it shouldn’t mean “no creed but Christ” or “Jesus only and therefore no Church” or “Jesus only therefore no Sacraments” for most Protestants do have a creed and a church and sacraments.
So perhaps those two central points already overlap a bit, or more than a bit. In fact they overlap so much that we can say, without trickery, that the whole reason for being a Catholic is to be the best possible evangelical Protestant.
What I mean by that strange statement is that the essence of evangelical Protestantism is to be one with Christ, to meet Christ, and that’s the best reason to be a Catholic. That’s the reason for the Mass, and the Eucharist, namely the Protestant thing of meeting Christ. That’s the whole point of the Catholic thing of the Church, and of the Sacraments and of the Saints and all of the rest. Take the Eucharist. Christ is not great because of the Eucharist, the Eucharist is great because of Christ. We Catholics don’t try to squeeze Christ out of the Church like orange juice out of an orange, Christ gave us the Church. We got the Church from Christ first of all. Only then do we get Christ from the Church because He put Himself into her. The Church is the servant, the messenger. The Church is Christ’s body, but the body is the head’s body. We don’t idolize anything. Protestants accuse Catholics of idolatry, ecclesiolatry, sacramentiology, Mariolatry, Christ is the only “idol.” The total “idola” or “icon” or “image” of God. We do not idolize, for instance, the doctrine of the Real Presence. It’s only a doctrine, though it’s a true doctrine. We worship Christ not doctrines about Christ. The Real Presence is the real presence of Christ. Christ alone is the absolute everywhere in Catholicism. Mary for instance, is holy only because of her relationship to Christ. She gave us Him by freely consenting to be His mother. And He gave us her, from the Cross. “Behold, your mother.”
Ecumenism Without Compromise - Peter Kreeft