First, the Church is catholic because Christ is present in her.
[snip long paragraph]
Secondly, The Church is catholic because she has been sent out by Christ
on a mission to the whole of the human race: All men are called to belong
to the new People of God. This People, therefore, while remaining one and only
one, is to be spread throughout the whole world and to all ages in order
that the design of God's will may be fulfilled: he made human nature one in
the beginning and has decreed that all his children who were scattered should
be finally gathered together as one...The character of universality which
adorns the People of God is a gift from the Lord himself whereby the
Catholic Church ceaslessly and efficaciously seeks for the return of all
humanity and and all its goods, under Christ the Head in the unity of
his Spirit.
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End Quote
So, I guess the answer to your question, is that Christianity is a
world religion, meant for everyone.
-alain