You may sometimes hear it said, "There are x Christians in Australia". I have put x for the number, because different people give different estimates. Or you may hear someone claim, “There are no Christians in any one of the denominations”. I'm not going to argue about such statements, because there is no sound basis to make an argument. What I will do, because I can be absolutely certain about this from the scriptures, is to state exactly what makes a person a Christian.
We do not say, “WE ARE THE ONLY CHRISTIANS”. However we do say, “WE ARE CHRISTIANS ONLY”.
The names of all Christians are written into the Book of Life (Rev 20:15, Php 4:3). That book does not exist on earth. Church registers and directories written on earth may tell us when people were born, married, and buried. They may tell us who are members of this church or that. But they are not the book of life. In order to find out who are true Christians, we may just as well consult the telephone directory as one of these books. Only the word of God can tell us the marks of a true Christian.