Who wrecked the unity, love, and harmony in the Garden of Eden? Well, Adam blamed Eve. Then Eve blamed the serpent, but the serpent didn't have a leg to stand on.
Even after raising so much Cain, the next generation didn't do so well either. Adam and Eve's boys tried to get along, but they weren't able. Allan Boesak put it this way: "What always strikes me in the story of Cain and Abel is how often the word 'brother' is used. Cain killed his 'brother.' God says it was 'the blood of your brother.' The killing was done to another human being, a child of God like you, breaking that sacred bond of common humanity."
Ever since then, human history has been full of people killing people. Today culture has advanced to mass shootings of strangers, suicide bombers, 'collateral damage,' poison gas, cruise missiles, and even mass vehicular homicide.
Of course, most human beings don't actually kill people, but the Bible says (in 1 John 3:15): "Anyone who hates a brother or sister is a murderer." Hatred (and might I add 'unkindness,') like murder, breaks "that sacred bond of common humanity." (There sure is a lot of hatred and unkindness spewing out in the 21st century).
The good news of Christianity is that Jesus came to make a way for people (who are not able in their own power) to experience healing and restoration from the mess we've made of our relationships with one another and with God. Jesus did that on the Cross by personally paying the debt for all the wrongs ever done against God and other human beings. Then He rose from the dead and came as the Holy Spirit, offering to forgive the sins of and to live inside any person who will surrender to follow Him in love and humility.
"Christ in you, the hope of glory." Where Eve's boys weren't able to do right, and where you've not been able to be perfectly "good" from within your deepest being; the risen Jesus wants to live His life of amazing love, in and through you.
Will you let Jesus do that? If so, you will immediately begin to experience amazing unity with other people (even strangers and/or people you disagree with) who are allowing the risen Jesus to live in and through them. What Eve's boys (and all the rest of us humans) could never do, Jesus is ready to do in and through you, now.
Then, when groups of people are willing to live and meet in that supernatural unity, it proves to those who see that unity in action, that Jesus is really from the Father! That's what Jesus prayed for His followers in John 17:21: "that all of them may be one, Father, just as You are in Me and I am in You. May they also be in Us so that the world may believe that You have sent Me."
That's what happened to me. As an agnostic, I walked in an informal meeting of Christians who openly loved one another in the Spirit. The caring community I saw among them, demonstrated to me the reality of Jesus Christ in a moment, and changed my life forever.
Jesus is able to reveal Himself to all sorts of people, if we will just push our arguments, our pride, our politics, divisions, our anger, our judgments, and our hatred, aside and let the living Jesus love others through us. Try it and see!