It's much more fundamental than any of the other posters have suggested. In the Bible, Jesus gives a directive to believers that's commonly known as the Great Commission which says
But the eleven disciples went into Galilee, to the mountain where Jesus had sent them. When they saw him, they bowed down to him, but some doubted. Jesus came to them and spoke to them, saying, "All authority has been given to me in heaven and on earth. Therefore go, and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things that I commanded you. Behold, I am with you always, even to the end of the age."
Matthew 28:16-20
Therefore, Christians have been commanded by God to "invest energy in trying to convince other people, not necessarily of their own religion, that their religion is good or "the best" or "the way"? Additionally, Christians believe that the only way to salvation is through belief in Jesus Christ and that we are to love our neighbor as ourselves. As a result, to want anything less than salvation for your neighbor is actually hypocritical.