Just some thoughts and scriptures that I've seen concerning unity and division in an ongoing study.
God divided light and darkness, land and sea, holy from the profane, nations and languages among other divisions seen in the scriptures.
Matthew 10:34 Think not that I am come to send peace on earth: I came not to send peace, but a sword.
Matthew 10:35 For I am come to set a man at variance against his father, and the daughter against her mother, and the daughter in law against her mother in law.
Matthew 10:36 And a man's foes shall be they of his own household.
In Ezekiel's temple when the measurements were being shown to him we see a division between the sanctuary and the profane place.
Ezekiel 42:20 He measured it by the four sides: it had a wall round about, five hundred reeds long, and five hundred broad, to make a separation between the sanctuary and the profane place.
Matthew 25:31 When the Son of man shall come in his glory, and all the holy angels with him, then shall he sit upon the throne of his glory:
Matthew 25:32 And before him shall be gathered all nations: and he shall separate them one from another, as a shepherd divideth his sheep from the goats:
Matthew 25:33 And he shall set the sheep on his right hand, but the goats on the left.
Throughout the NT, there were divisions when people could not agree on whom Jesus is.
John 7:40 Many of the people therefore, when they heard this saying, said, Of a truth this is the Prophet.
John 7:41 Others said, This is the Christ. But some said, Shall Christ come out of Galilee?
John 7:42 Hath not the scripture said, That Christ cometh of the seed of David, and out of the town of Bethlehem, where David was?
John 7:43 So there was a division among the people because of him.
John 9:16 Therefore said some of the Pharisees, This man is not of God, because he keepeth not the sabbath day. Others said, How can a man that is a sinner do such miracles? And there was a division among them.
The world's idea of unity is not the same as God's instruction for unity.
Philippians 2:1 If there be therefore any consolation in Christ, if any comfort of love, if any fellowship of the Spirit, if any bowels and mercies,
Philippians 2:2 Fulfil ye my joy, that ye be likeminded, having the same love, being of one accord, of one mind.
Unity starts with Christ being the head, keeping God first in all things and not leaning on our own understanding.