By virtue of God's gracious covenant, men not only have a covenantal union with Christ, but enjoy covenantal communion with Him. This is why we give baptism to our children. Any branch in union with the vine enjoys communion with that vine. If there is no communion, there is no union. This is the principle followed in our church discipline.
Communion is the unmistakable mark of union.
Where communion is cut off, there is no union with the body. It seems to me increasingly clear that such is the Bible's teaching. Now, here we run into a problem. The historic Reformation creeds and confessions acknowledge the legitimacy of covenant baptism but deny the legitimacy of covenant communion. I am well aware of the seriousness of disagreeing with any confession of faith that has received the approbation of the Christian Church.