"They Say I Won't Go to Heaven!"

Are we told specifically to remember God and reflect on His attributes? What is "double-mindedness" exactly? My friends are telling me I won't go to heaven, because I don't go to church. Are they right? Is it true that we (the people) are the church? How do we best understand the warnings to the churches in Revelation? What about people who never hear the gospel? And what about babies who pass away?