As Long As One Is Sincere, Does It Matter What One Believes?
The Hindu is sincere, the Moslem is sincere, so are the followers of Buddhism and Judaism, but, not a one of them are saved in these beliefs. But you say, wait a minute, these don't count because they are not "Christian" -- if one is sincere in the "Christian religion" it doesn't matter what you believe. If this is your reply, then you admit it does matter what one believes, even though he is sincere.
The same standard of authority applies to all, regardless of what one believes in religion. That authority is God's Word, the Holy Bible. To those who do not believe in Jesus the Christ, we read where Jesus said: "...I am the way, the truth, and the life: no man cometh unto the Father, but by me" (John 14:6). Salvation cannot be found outside of Jesus. "Neither is there salvation in any other: for there is none other name under heaven given among men, whereby we must be saved" (Acts 4:12).
On the other hand, not all those who believe in Jesus will be saved, even though they are sincere. Jesus said, "Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven. 22Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works? 23And then will I profess unto them, I never knew you: depart from me, ye that work iniquity" (Matt. 7:21-23). Jesus talks about people in these verses who were believers. These were even believers who worked for Jesus -- they were sincere. But, the Lord's answer to them was "...I never knew you: depart from me, ye that work iniquity."
Sincerity is not enough. One can be sincere but still be wrong. Were the five foolish virgins sincere (Matthew 25:1-11)? They made some preparation, but not enough.
One must be sincere, but at the same time, must follow the teaching of Jesus. One must follow His Way, not what we think is right. Are you following His Way? Study and learn.