This expression is found in 1 Cor. 10:21, and was written before any divisions had taken place in the Church, which was formed by the descent of the Spirit on the day of Pentecost. (1 Cor. 12:13.)
The Lord's table then has two marks: First, the Lord must have set it up.
Second, the apostles' doctrine and fellowship must characterize it. (Acts 2:42.1
The Church is not a voluntary gathering of Christians, but a unity formed by the Spirit uniting believers to Christ the Head in heaven. The one loaf on the table is the scriptural symbol of that unity. (1 Cor. 10:17.)