Why do some believe you have to be a part of some building to enter heaven?

Answer:

I know of no congregation which states you need to be a member of a particular location or building in order to enter heaven. I can't answer your question directly since I've never heard the argument being made.

Christianity is a way of life and part of that way is joining with other Christians in your area to form and be a part of a church. This is not an option but a command of our Lord. Some aspects of worship cannot be done without being a part of a local group. For example, the partaking of the Lord's Supper requires sharing it with others of like faith. "The cup of blessing which we bless, is it not the communion of the blood of Christ? The bread which we break, is it not the communion of the body of Christ? For we, though many, are one bread and one body; for we all partake of that one bread" (I Corinthians 10:16-17). Singing's purpose is to teach others, "speaking to one another in psalms and hymns and spiritual songs, singing and making melody in your heart to the Lord" (Ephesians 5:19). But a congregation isn't the building but the people who gather together to work and worship together.