The first thing that must be clear in our hearts is that we are brought into the family of God by birth. "Unless one is born again, he cannot see...cannot enter the kingdom of God" (John 3:3,5). The kingdom of God is where God rules by the Spirit. A natural son is a son because he received life from his father. So it is in the family of God. We are sons of God because we receive our life from Him. Jesus said that the New Covenant was a covenant in His blood (Luke 22:20). The life is in the blood, and He poured out His life that we might live.
Herein lies the reason that the family of God did not exist in the Old Covenant. The sacrifice for sin had not yet been paid, so men could not yet partake of His life. Under the Old Covenant, man had his life from Adam his father, but that life was a life of death: that is, separation from God. The law was given to hold the nation of Israel until the time of Christ, but death reigned from Adam to Moses, and from Moses to Christ. Not until Christ came did life appear. Christ came to give us life, and that life was so that we could be sons. This is an intimate relation that brings us into union with God.
Let us not pass over the implications of these truths too quickly. The intimate relationship of a Father with His sons was not possible in the Old Covenant. In that time God dealt with a nation, not a family. Now through new birth we have been brought into the family of God. We may know these words, but has the reality of them gripped our hearts? We have been brought near to God. We are no longer slaves, but friends! We are members of the household of God--sons and daughters.
This truth and all that follows from it form the framework of our relationship with God, and with each other in His family. In a nation, people can function and keep their distance. They do not live in the same family. But since we live in the same family, there is no such thing as "keeping each other at arm's length." Relationships must be pure. Attitudes must be right. A wrong relationship grieves the Holy Spirit, and since each family member is connected by the same life, all of the members will feel that grieving.
Paul brings out the same thought in the context of the "body of Christ." "And if one member suffers, all the members suffer with it; or if one member is honored, all the members rejoice with it" (1 Corinthians 12:26). The members of the body are connected, so they are not independent. This is not just a concept, but a spiritual reality, and it is true because we are put into the body by His life (1 Corinthians 12:13), just as we are born into the family by His life. We are connected to the Head of the body, and to the Father, by the very life of God. In both relationships, everything is dependent on an intimate union with God by the Spirit. We are connected to each other by the same life.