1 Corinthians 12
27 Now you are the body of Christ, and each one of you is a part of it.
15 The Son is the image of the invisible God, the firstborn over all creation. 16 For in him all things were created: things in heaven and on earth, visible and invisible, whether thrones or powers or rulers or authorities; all things have been created through him and for him. 17 He is before all things, and in him all things hold together. 18 And he is the head of the body, the church; he is the beginning and the firstborn from among the dead, so that in everything he might have the supremacy.
Paul was addressing believers. This means that we, the believers in Christ, are his "body," which is the church. This is because we, as believers, have his Spirit within us. All followers of Christ make up the true church of Christ.
This is so simple and so beautiful in the fellowship and oneness it gives Christians that its sad that we're so unable to look past denominations and labels and just see each other as brothers and sisters in Christ. All you need is Jesus in order to be a Christian that belongs to the "true church".