It is strange but true that most people — even the great majority of religious people — do not know what a church is. Ask the average person what a church is, and they’re apt to reply: “Well, anybody knows that! A church is a building where people go to worship God.” But this is not correct. The word translated church, in our Bibles, simply means assembly. A church is not a building, but the assembly that meets in the building. Technically, a church is not even a religious gathering, for the same word is used in Acts 19:32 of a riotous mob which had assembled at Ephesus, and this verse says that this assembly was confused and that “the greater part knew not wherefore they were come together.” Perhaps this could apply to many a church today, but the point is that a church is not a building but an assembly of people.
The church of which the Bible has most to say is “the Church of God, which He hath purchased with His own blood” (Acts 20:28), and St. Paul calls the church of this present dispensation, “the Body of Christ,” or “the Church which is His Body” (I Cor. 12:27; Eph. 1:22,23).
Men cannot join this Church by water baptism or any other religious rite, but only by faith in the Lord Jesus Christ. With regard to believers in Christ St. Paul declares: “By one Spirit are we all baptized into one Body” (I Cor. 12:13). And in Rom. 12:5 the Apostle says that “ye, being many, are one body in Christ.”
Many sincere people have had their names on local church rolls for many years before learning this great truth — that the true Church of God is not a building, but the assembly of those who trust in Christ as their Savior. Doubtless, people in and out of many of the religious organizations we call churches belong to this one great Bible Church, while others, with all their religious profession, do not. The question is: Have we sincerely trusted in Christ as the Savior who died for our sins? source