At the center of history stands the cross of Jesus Christ. The vertical dimension is restated in Ephesians 2:13: Jesus came down to meet us where we were (the grave) and brought us up to glory, into relationship with God. But there is also a horizontal dimension to the cross, which depicts Jesus, arms stretched wide, reaching out and embracing all those reconciled to God, bringing them into community. Thus the church is called to be in community with each other and to bring others into that community, carrying on the mission of Jesus. That means, says Paul, that we have to recognize the walls that Jesus has broken down and not rebuild them. 
Scripture:  Ephesians 2:11-22