Religious people love hierarchy.  They delight in being somewhere on a ladder which they can climb by their own efforts.  They also think that there are some people higher than them and some who are lower.  In Jesus’ day, the Jews considered the priests to be higher, and the chief priests to be very high.  They also considered women and children to be much lower than the men.  The Gentiles were the lowest of all.
 
Jesus taught differently, and the apostles reinforced His message - that all those who come to God through Jesus Christ are equal in His family.  Poor slaves were as equally valued by God as their wealthy masters; Gentiles were as welcome as those who had Jewish ancestry; women have the same inheritance rights in God’s kingdom as men; and nobody should despise children.  Abraham looked forward to that day (John 8:56).  He was a man of faith, looking forward to the time when God’s sacrifice would atone for the sins of all people (Genesis 22:1-18).  So all who believe in Jesus are the spiritual descendants of Abraham, and share an eternal inheritance with him.  

“All one in Christ Jesus” is a big statement.  The oneness does not come from our common past or present circumstances, but because we have a common future with Jesus.  We are not ‘all one’ because of some arbitrary equality which makes us as good as each other, because all have sinned and fallen short of God’s standard (Romans 3:23).  We are ‘all one’ because we have all admitted our sinful nature, rebellious attitudes and wicked behaviour, and we have all been forgiven (1 John 1:7) through Jesus’ sacrifice in our place (1 Peter 2:24).
 
Our human nature is full of pride and self-centeredness.  It instinctively dislikes the idea that anybody who is not like us can be a friend of God.  But that old nature speaks falsely.  The truth is that there are no barriers of gender, race, religious background, social class, or financial status that can separate those who have put their trust in the Lord Jesus Christ from Him.  We are all one in Him.  And so we need to find ways to express that unity - in the workplace, the community, internationally and across the vast range of denominational preferences. It will be normal in heaven (Revelation 7:9-10); it needs to be normal until we get there too.