Hebrew society was basically tribal in nature, composed of huge extended families that took care of their own. Although based on God's holiness, all the commands to love are concerned with those within the tribe: family, relatives, countrymen, and neighbor. Those outside the tribal network were also outside the network of care and concern, left to God's providence.
In the portion of the Sermon on the Mount which we just heard, Jesus repeats the ancient law and then expands it, inviting his disciples to share in God's care for everyone. For Jesus, there are no insiders or outsiders. Everyone is to be cared for.