“Those who come to the house of prayer are people afflicted with all sorts of spiritual defects–often wavering in faith, weak in love, dull in awareness. They come to the house of prayer from the world, with the unholy fountain of churning sins in their hearts. They bring with them the memories of all sorts of shortcomings. The more spiritual they are, the more serious is their self-indictment. They are called “saints,” but they ask themselves instinctively how anyone could possibly include them among the “saints.”
And yet the assembly is “a communion of the saints.” Observe how the apostle always addresses the churches to which he writes as those “called to be saints,” in Corinth, in Ephesus, in Colossae, in Thessalonica. If they indeed were not, how then would they be distinguished from the world? Why then would they here constitute the “congregation?” If they were equal with the people of the world and one with them, what kind of self-elevation and contempt of others would it be if they should nevertheless call themselves a holy congregation?
There is an apparent contradiction here–a contradiction between the sign of spiritual worth with which they gather and the lack of such worth in their hearts that they are mourning. They indict themselves and God declares them innocent. For whether the world slanders them and Satan sets himself against God’s elect, the fact remains that they as the congregation of the Lord, as the communion of the saints, must assemble. This contradiction, this opposition can be overcome only through the name of Christ. Outside of Christ there are no saints, there is no congregation, and thus an assembly of the congregation is unthinkable. Furthermore, outside of Christ there is no worship of and no communion with God.”
-Abraham Kuyper, On Worship.