When Paul wrote "you are the body of Christ" (1 Cor 12:27) or "in Christ we who are many form one body, and each member belongs to all the others" (Rom 12:5) what did he mean? What exactly is the "Body of Christ"?
We take a lot for granted. For example, in the two places where Jesus spoke about the "church" (ekklesia) we assume we know what He was talking about. It's obvious isn't it? He was referring to groups of people who meet in tidy buildings, in rows of chairs neatly set out; following the same order of services they have since the apostles (4 hymns, 2 readings, an exhortation, prayers, breaking of bread and announcements); with elected arranging brethren, presiding brethren, rostered organists, etc.
Except that's clearly not what Jesus understand by "church"/ekklesia. Even if He was thinking 1800 years into the future His audience obviously couldn't have had that vision in their minds when they heard Him speak of church/ekklesia.
So what did He mean? When Jesus referred (only twice) to the ekklesia He used a word which was used in the LXX Greek translation of the Hebrew Bible to refer to Israel as God's community. It was a word which meant (to a Jewish audience) "the people of God", and it was a word which included the whole community. So in Matthew 18 when Jesus spoke about being reconciled with a brother, He said we should first enlist the help of a trusted friend, if necessary get one or two others involved, and then if really necessary we should get the help of the whole community of God's people in order to be reconciled with a brother.
So we find in the Hebrew Bible that on important occasions when God's people presented themselves before God that they did so as HOUSEHOLDS. Passover was to be kept by the whole household. When the tithe was presented to the Lord the whole household had to be there to eat together "in the presence of the Lord" (Deut 14:22-27). When the Philippian jailer was converted his whole household was baptised and joined the community of God's people (Acts 16:33). The (unbaptised) children of believers are "holy" (1 Cor 7:14).
Scripture is screaming out to us in these verses and elsewhere that God is interested in families, households and communities. The community of God's people includes new converts, those who have passed down the Word of God for generation after generation, parents, their children who are also "holy", single people, the Sunday School, the Youth Group, the elderly with dementia in nursing homes, and all those in the care of God's people. Together they make up the "congregation of Israel", the ekklesia, the community of God's people, the Body of Christ.