Most people are most comfortable with exclusion than inclusion. From an evolutionary point of view, it makes sense: tight knit communities seems to be best served by belonging stemming from certain processes of exclusion. But though our human psychology may have been formed by culturally-evolved processes, we're not people of evolutionary development. We are people of baptism, people of faith, people of God - and we are called to inclusion, not exclusion.
I saw a meme recently that explains it as follows:
The Bible is clear: Moabites are bad. They were not to be allowed to dwell among God's people (Deuteronomy 23). But then comes the story of Ruth the Moabite, which challenges prejudice against Moabites.
The Bible is clear: people from Uz are evil (Jeremiah 25). But then comes the story of Job, a man from Uz who was "the most blameless man on Earth."
The Bible is clear: no foreigners or eunuchs allowed (Deuteronomy 23). But then comes the story of an African eunuch welcomed into the church (Acts 8).
The Bible is clear: God's own people hated Samaritans. But then Jesus tells a story of Samaritan who was good, and who acted mercifully when the religious folk refused to.
The story may begin with prejudice, discrimination, and animosity, but the Spirit moves God's people towards openness, welcome, inclusion, acceptance, and affirmation.
As Peter finally says in Acts 10: "I truly understand that God shows no partiality."