"He is the beginning, the firstborn from the dead, that in everything he might be preeminent. For in him all the fullness of God was pleased to dwell, and through him to reconcile to himself all things, whether on earth or in heaven, making peace by the blood of his cross." (Colossians 1:18-20 ESV)
Christianity is often seen and portrayed as being exclusive rather than inclusive, and culturally narrow rather than ethnically broad. And yet, it is precisely because Christianity is universal that it is therefore exclusive. It is because Christ's work is so complete that all other ways are only partial at best. Herman Bavinck explains,
"Christianity is therefore the absolute religion, the only essential, true religion. It does not grant that other religions are of almost equal worth alongside of it. It is, according to its nature, intolerant, even as the truth at all times is and must be opposed to falsehood. It will not even be satisfied by being the first of the religions, but it demands to be the only, true, full religion that includes and fulfills all that is true and good in other religions. Christ is not a man alongside of others, but the Son of Man, who by the power of the resurrection was shown to be the Son of God, according to the Spirit of holiness, and received of the Father a name above every name, so that in that name every knee should bow
and every tongue confess that he is Lord, to the glory of God the Father [Rom. 1:4; Phil. 2:9-11].
"In this unity is, of necessity, implied the universality of the Christian religion. While there is but one God; he is the Creator of all things [1 Cor. 8:6]. Because there is only one Mediator between God and man, he is the Savior of the whole world [1 Tim. 2:5]...
"The Holy Scriptures proclaim this universality of Christianity in the clearest and most beautiful way. The Father loved the world. Therefore, he sent his only begotten Son, that whoever believes in him will not perish but have everlasting life [John 3:16]. In that Son God has reconciled the world to himself...
"The world, which was made through the Son, is also destined for the Son as its heir [Heb. 1:2]. Someday, all kingdoms will become the kingdom of our Lord and his Christ [Rev. 11:15]."
~ Herman Bavinck, Sacrifice of Praise (Hendrickson, 2019)(Dutch, 1901)
Because there is one humanity, and because there is only One who can redeem humanity, there is only one true religion, which as Bavinck notes, is "the only, true, full religion that includes and fulfills all that is true and good in other religions."