Jesus' sacrifice

It is the central tenet of Christianity that God sent his only begotten son amongst mankind as a ransom for man’s sins. This should have meant that sin in mankind, which entered mankind through the original sin of Adam in disobeying God (and eating the forbidden fruit), the wages for which was death, would have been cleansed by the sacrifice of Jesus Christ. This should have resulted in everlasting life for mankind since then. However, it appears to me that the ransom of Christ was hijacked by the Church which said that mankind would be assured of everlasting life only if it believes in Jesus Christ. Has Christ’s sacrifice been in vain?

My basic question is whether believe is sine-qua-non for connecting to Christ?

As far as Christianity is concerned, it is a truism that “Jesus died on the cross for our sins”. But the Church and Missionaries still say all of us are sinners. So what was Jesus’ sacrifice all about? For the Church and Missionaries it is about believing Jesus, as if his teachings weren’t good enough to transform us. Further, the Church thinks we have to couple believe with becoming members of the one true church. The missionaries think we have to denounce all religions except Christianity (the pernicious conversion enterprise!). I think Jesus himself meant it is about awakening to the divinity within and without us – as so many of the best teachers of mankind taught. The only “sacrifice” Jesus made and all of us need to make for everlasting life is to reject the hold of the material upon us. Jesus was an example. You don’t need to believe in examples. You have only to understand it.