Acts 10:34, NKJV. "Then Peter opened his mouth and said: 'In truth I perceive that God shows no partiality.'" Romans 2:11, NKJV says, "For there is no partiality with God."
Why does God condemn favoritism? Because it reveals a destructive double standard. It's in the Bible, Malachi 2:9, TLB. "Therefore, I have made you contemptible in the eyes of all the people; for you have not obeyed Me, but you let your favorites break the law without rebuke."
Favoritism devalues people for whom Christ died and indicates an ignorance of God's values. It's in the Bible, James 2:1-4, TLB. "Dear brothers, how can you claim that you belong to the Lord Jesus Christ, the Lord of glory, if you show favoritism to rich people and look down on poor people? If a man comes into your church dressed in expensive clothes and with valuable gold rings on his fingers, and at the same moment another man comes in who is poor and dressed in threadbare clothes, and you make a lot of fuss over the rich man and give him the best seat in the house and say to the poor man, 'You can stand over there if you like, or else sit on the floor'—well, judging a man by his wealth shows that you are guided by wrong motives."
It is dangerous and unwise to show favoritism in a family. It's in the Bible, Genesis 37:3-4, TLB. "Now as it happened, Israel loved Joseph more than any of his other children, because Joseph was born to him in his old age. So one day Jacob gave him a special gift—a brightly colored coat. His brothers of course noticed their father's partiality, and consequently hated Joseph; they couldn't say a kind word to him."