"You have heard that it was said, 'You shall love your neighbor and hate your enemy But I say to you, love your enemies, and pray for those who persecute you, that you may be children of your heavenly Father, for he makes his sun rise on the bad and the good, and causes rain to fall on the just and the unjust. For if you love those who love you, what recompense will you have? Do not the tax collectors do the same? And if you greet your brothers only, what is unusual about that? Do not the pagans do the same? So be perfect, just as your heavenly Father is perfect. (Mt 5, 43-48)
God the Father is the model for our earthly life and as children of this Father we are asked to imitate Him.
In this passage three types of people are presented as models: tax collectors, pagans and God the Father.
Tax collectors love in return only those who love them. They could be anybody: Jews, Romans, slaves etc. If they love the tax collectors then they are loved in return.
Pagans greet their brothers. Pagans keep to their own kith and kin. They do not move out of their group, or race etc.
Love and greetings are expressions of relationships. These two relationships are exclusive relationships. These two relationships are self-centered, limited, controlled.
God the Father loves everyone. He has no distinctions and differences. God does not even look into the justifiable differences. The usual differences are between good and bad; just and unjust. No one will be really sad (in practice) when a wicked man is punished. In the same way no one will be hurt when an unjust man is penalized. One would even say that he (the offender) deserves the punishment.
But God loves everyone. When giving rain and sunshine he does not look at the colour, caste, creed, nationality, and even moral differences (good/bad; just/unjust).
Perfection of God here is not in the moral Perfection (which is impossible to attain) but perfection in loving everyone without looking into the differences. “Be merciful, just as your Father is merciful”. (Lk 6,36)