I support Ecumenism. It is a Beautiful Spirit-Led Movement toward Christian Unity. Ecumenism is firstly only between (1) Baptized Trinitarian Christians and (2) those who confess Jesus Christ as Lord and Savior, and Son of God, etc, which the Bible says no one can do without the Holy Spirit; Ecumenism also does not mean either doctrinal indifference nor some kind of absorption into a mega-Church. Rather, it means that, through prayer, through theological discussions etc, among Bishops, Priest and Pastors, and so on, with Christian Charity, the Churches gradually walk together on the path toward full re-union.
For the Catholic Church, Vatican II's Unitatis Redeintegratio ("Restoration of Unity") said this: "1. The restoration of unity among all Christians is one of the principal concerns of the Second Vatican Council. Christ the Lord founded one Church and one Church only. However, many Christian communions present themselves to men as the true inheritors of Jesus Christ; all indeed profess to be followers of the Lord but differ in mind and go their different ways, as if Christ Himself were divided.(1) Such division openly contradicts the will of Christ, scandalizes the world, and damages the holy cause of preaching the Gospel to every creature.
But the Lord of Ages wisely and patiently follows out the plan of grace on our behalf, sinners that we are. In recent times more than ever before, He has been rousing divided Christians to remorse over their divisions and to a longing for unity. Everywhere large numbers have felt the impulse of this grace, and among our separated brethren also there increases from day to day the movement, fostered by the grace of the Holy Spirit, for the restoration of unity among all Christians. This movement toward unity is called "ecumenical."
Those belong to it who invoke the Triune God and confess Jesus as Lord and Savior, doing this not merely as individuals but also as corporate bodies. For almost everyone regards the body in which he has heard the Gospel as his Church and indeed, God's Church. All however, though in different ways, long for the one visible Church of God, a Church truly universal and set forth into the world that the world may be converted to the Gospel and so be saved, to the glory of God."
https://www.vatican.va/archive/hist...ecree_19641121_unitatis-redintegratio_en.html
Islam is not included in this, despite what some say, since they don't confess Jesus Christ as Lord and Savior, nor are Baptized and Trinitarians. But Muslims are monotheists though and profess to worship the God of Abraham, just like the Jews. What applies to Jews, Muslims etc is called "inter-faith dialogue" and substantially different from Ecumenism itself.
Jews and Muslims have an advantage over Hindus, most of whom are polytheists, and Buddhists, most of whom don't believe in a personal God. But of course, all Jews, Muslims, Buddhists and Hindus can only be saved by faith in Jesus Christ.
The Catholic Catechism says on that: "
161 Believing in Jesus Christ and in the One who sent him for our salvation is necessary for obtaining that salvation. "Since "without faith it is impossible to please [God]" and to attain to the fellowship of his sons, therefore without faith no one has ever attained justification, nor will anyone obtain eternal life 'But he who endures to the end.'" Taken from:
http://www.scborromeo.org/ccc/para/161.htm So it is clear Muslims etc are not saved.
God Bless.