I know that the obvious boundary in the Bible is Old/New Testaments. I prefer to make the split Genesis 1-11 and the rest. Genesis 1-11 contains those stories we might say are universal. I read them and understand that I am being described, as is the world, and our universal, human predicament. (E.g. Noah and the flood, here.) God's response we read about from Genesis 12. (Here.) The universal predicament of humankind brings a particular response, God's call to Abraham and Sarah to leave their secure home and to wander the promised land in faith, and God promises that through them all the families of the earth shall be blessed. (Gen 12:1-3.) Paul makes much of this (Rom 4 & Gal 3) including that marvellous claim that this blessing to the Gentiles is the Gospel! (Gal 3:8) This blessing is manifest in the union of humankind through the dismantling of the barriers that divide us. (Acts 2:1-11 compare Gen 11:1-19 see here, here, here) These barriers that divide us are universal, and our universal predicament. They have as their root human envy, rivalry, arrogance, and the violence to maintain and create dividing walls, all to be found in increasing intensity as we read through Gen 1-11. Christ saves us from this predicament, by bringing us, Jew and Gentile, together through the cross. (Ephes 2:16, but Jew/Gentile as paradigms of all dividing walls, see Gal 3:27-29.) And that is the extraordinary thing. Crosses maintain the barriers. Jesus, accused blasphemer, crucified to maintain the wall that divides, brings us together through that very instrument of violence and division. Through Jesus, handed over into the hands of sinners yet vindicated in the resurrection, Satan's ruse (here) is unmasked for those with eyes to see. That which divides us - the accusations, the pride, the rivalry, all of it - and that crucified Christ, is now crucified to us so that it is Christ who lives in us. (Gal 2:20)
This is why St Paul rails against division and the sort of attitudes and behaviours that cause it. (1Cor 1:10-17, and notice he then launches into his great proclamation of the power of the cross, 1:18-25. See also Rom 12:3; 1Cor 8; 11:17-22; Gal 5:16-26.) Division in the church insults the Gospel itself, for our unity in Christ is integral to the Gospel, not an added on extra. If you don't believe me search and see how often Paul links poor behaviour and its renewal to the death of Christ and the death of our old nature. (E.g. Col 3:5-17.) And notice how Paul's explanation of faith, law, grace, and justification can lead to his reflections on God's promise to Abraham. (See Rom 1-3 leading into Rom 4, and then keep reading into Rom 5! Also, Gal 2:15-21 leading into Gal 3.)
In an age of intensifying polarization, with accusation and counter-accusation, here is a mission for the traditional church. Traditional churches eschew fads, do not have a cause derived from Jesus (that is a cause having a life apart from Jesus) and are wary of the heightened emotionalism and easy judgements of the mob. Nurturing this and living into our unity in Christ, while still holding a variety of opinions on different topics (often divisive topics in the world around us) is not an easy road. But because it is the gospel itself it includes cross-work (Mark 8:34-35) but also freedom and human dignity, and the whiff of resurrection.
