3:102 O You who have chosen to be graced with belief! Live upright being mindful of God in a manner befitting to Him. Let not death overtake you but that you are Muslims.
3:103 You must hold fast, all of you together, to the Bond of God and be not divided into sects. (The Bond or Rope of God is the Qur’an which is an Unbreakable Support 2:256.) Remember God’s Favour upon you when you were enemies and, almost overnight, He brought mutual affection in your hearts. Thus, you became brothers and sisters by His Grace. And recall that you were on the brink of the pit of fire, and He saved you from it. (Various tribes used to attack one another, and personal enmity plagued them.) This is how effectively God has made His messages clear for you to journey on the lighted road. [6:165, 30:31-32, Huda = Guidance = Walk the right path = Travel on a lighted road]
3:104 Let there be a community among you that invites to all that is good, advocating virtue and deterring vice. They are the truly successful.
[Verses 2:143, 3:110 and 22:78 assign this duty to the entire Muslim community. Ma'roof = Virtue = Kindness = All that is good = Declared Ma’roof by the Qur’an. Munkar = Vice = Evil = All that is wrong = Declared Munkar by the Qur’an. 2:143, 3:109, 23:1, 61:2-3]
3:105 Do not be like those who became divided and disputed after all evidence of the Truth had come unto them. For, they have incurred a tremendous suffering.
[Sectarianism, schism and division stand in the way of unity of all mankind. Bayyinaat = Clear evidences. 6:159-160, 30:32, 42:43]
We stopped doing the above a long time ago and mankind has been suffering as a result.