First of all, whether a thing is true or not is not determined by the percentage of people who believe it. What you need to decide is not how popular Jesus is but whether his claims about himself (I am the bread of life, I am the resurrection and the life, I am the way, the truth and the life) are true. If Jesus did fulfill the messianic prophecies, if he did work unprecedented signs, if he was in fact resurrected from the dead, then you ought to worship him and be a Christian.
Second, your feeling that the number of Christians is decreasing is definitely NOT TRUE. No expert who studies the overall number of believers in Christ will agree with your feeling. It is simply false. Now, it is true that in some countries, such as in the US and in large parts of Europe, the percentage who believe has decreased. In the case of Europe, the absolute number of Christians has decreased over the past 100 years or so. In the case of the United States, the percentage of believers has decreased, but the absolute number of believers has held roughly steady, as the population has increased.
True, but the numbers of believers in Christ has exploded in Africa and in Asia. It has been estimated that there are between 100,000,000 and 150,000,000 Christian believers in China. Millions are converted to Christ ever year in Africa. The number of Christian believers in Central and South America has also rapidly expanded.
The Pew Research organization has published the following estimates for the number of Christians in the world:
Of course, the percentage who are Christian would depend on your definition of a Christian. I have a question: Did this person mention where he/she found the study, and did they explain their definition of Christian?
When I talked about the number of “Christians” in the world, I was using data on people who self-identify as Christians. One thing I am absolutely sure of, without needing to do the research, a lot more than 10% of Mexicans self-identify as Christians! I would bet you that it is over 80%. OK, just for fun, now that I got that far in my e-mail, I am going to go away for a few minutes and do the research, and when I come back, I will report to you what I found. See you in a few minutes.
OK, I am back. I did a little research and found a recent study from the Pew Research Organization. They found in a recent survey that 80% of Mexican people self-identify as Catholic. I did not see the numbers, but I have been to Mexico many times, and I am going to guess (and be aware that this is truly just a guess and please do not quote me!) that at least half of the rest will self-identify as another sort of Christian, such as Pentecostal or Evangelical. In fact, that may be what the person you are referencing to is doing. In other words, this person may be quoting something like this: 80% Roman Catholic, 10% other Christian and 10% all other groups. So, my guess is that this person believes that Catholics are not Christians!!!! You can decide for yourself about what this person is doing!
Bottom line, somewhere more than 90% of Mexican people self-identify as Christian, which is higher than in the United States for sure. This will be true throughout Latin America. Now, you can question the quality of the Christian lives of these people, and that may be a very valid thing to question, but in the statistics I was quoting in that article, I was talking about people who identify as Christian.