This is a question that seems to cause grumbling, but that’s usually because those discussing it haven’t defined their terms, and the preposition “for” is very slippery. As such, these are all true…

• Church is for everyone!
  It’s a gathering to sit under and respond to the word of the living and true God. The God of the universe. When Jesus comes back and raises everyone from the dead, they’re all going to be gathered (churched) around him and respond Philippians 2 style. So they should be in local churches now too.
• Church is for Christians!
  This is a true, although narrow, use of the term “for”. Technically, church “is” Christians. Church is the family/community/flock-of-an-under-shepherd gathering of those who hear and respond to Jesus as Lord. It’s a Christian “thing”, so yeah, it’s for them by the simple fact it is them.
• Church is for Christian encouragement and perseverance!
  This takes the previous point and gives it some flesh. If church is the gathering of those under Christ, then that gathering should support and equip those very ones to remain in Christ, in a fully Heb 3:13 way. In other words, if you’re going to get people together who exist on the basis of Jesus’ words, REMIND THEM to keep going!!
• Church is for gospel proclamation
  See, this is really the common thread. The gospel is a message of the global king. Its content describes its extent. It’s a message for everyone, especially those who have already believed it.

So, if church is for everyone, especially Christians… how should you design your meetings?