Are there all kinds of different religions in heaven like there are on earth?
In order to more effectively give the answer to this simple question, let me begin by speaking to what religion is and to explain its real purpose.
The very reality of “religion” is to connect or reconnect people to God, bringing them together (as the etymology, or roots of this word imply). In our understanding of Catholic Christianity, religion is revealed to us by God as the way that He aids us in being drawn into the life, friendship, and/or communion with Him and to remain in relationship with Him throughout this life, through death, unto eternity. True religion is not something that human beings have the capacity to invent – to say it bluntly, who among us limited (and fallen) creatures that we are can claim to have the means to connect ourselves to He that is infinite and perfect? By necessity, the reality of religion is therefore given to us from God so that He (in the person of Jesus Christ, who is “the way, and the truth, and the life” who alone brings us to God the Father [John 14:6]), can bring us into communion with Him. Thus, the “acts of religion,” if I can use that term to describe the things that human beings do to enter into and to remain in relationship with God, are shown to us first by God. They are meant for our living in this world so as to as help us to receive from Him and to learn to live in the perfect communion that only God can give for eternity.
Switching gears then from earthly living of religion to the life of heavenly perfection, it is of first note that in the fullness of the eternal life of heaven in which we have placed our hope in God, there will no longer be any need for us to exercise our free will “in religion” to remain in Him, as our choice from this life will be forever perfected in the fullness of that relationship in His perfect presence – and will therefore be both perfectly free and in perfect union with Him. In other words, in heaven the realities of religion will cease to exist insofar as the earthly goals of religion (perfect love and union with God and neighbor) will be fully realized and no longer need to be “practiced” or “learned;” we will live them perfectly. Consequently, the answer to the initial question of whether or not there are many religions in heaven is a simple “no;” as no religion will be necessary. That simple answer being as it is, note well – not all religions are the same (as people often like to say today so as to avoid tension); likewise, not all religions are a true way to heaven. It is of unspeakable importance to say that only one religion is revealed by the Triune God – and that is the religion that was first given by God to the chosen people of Israel and was fulfilled and perfected in what is revealed and accomplished by Jesus Christ; and it is the fullness of this religion that fully subsists in the Catholic Church. While there are thousands of expressions of religion (both inside and outside Christianity), there is one religion that can claim to have been fully revealed by God in the person of Jesus Christ, and that is the religion given by Jesus Christ to the Apostles which has been handed down through 2000 years of life in the Catholic Church.
This reality of the Church in the world as the true and complete means of religion will, however, have its proper end in heaven, when we will no longer need a way or means to God, but will live the fullness of the reality that the Catholic religion intends to bring about in those who embrace the truth, seeking to practice it and live it now in every moment. Does this mean only Catholics go to heaven? By no means! However, the Church does exist for the salvation of the whole world – including non-Catholics, non-Christians, atheists, and any others. We who have received the Catholic faith in its fullness will be judged accordingly – as to the one who has been given more, more will be required (see Luke 12:36). This includes our need to share our faith by not being afraid to live it at all times, to explain it rightly when asked, and to invite others to “come and see.” It is not our place to force religion; however, it is our definite task to fearlessly witness to it – that others may see our lives and be drawn toward a relationship with the Triune God (or as Jesus says in Matthew 5:16, we are to let our light shine that others may see our good works and give glory to the Father in heaven) – as He desires ALL to have a right share in that perfect life and love of heaven.