The Catechism in Questions & Answers

286. What does the commandment to love one’s neighbour demand?

The commandment requires human beings to treat all other human beings with love. It sets clear limits to egoism.
In the parable of the Good Samaritan (cf. Luke 10: 25-37), Jesus illustrated that loving one’s neighbour involves being merciful and acting accordingly.
Just how seriously Jesus meant these words can be inferred from His exhortation to even love one’s enemies.

“You have heard that it was said, ‘You shall love your neighbour and hate your enemy.’ But I say to you, love your enemies, bless those who curse you, do good to those who hate you, and pray for those who spitefully use you and persecute you, that you may be sons of your Father in heaven.”
Matthew 5: 43-45