This is a summary of Aquinas's division of love of neighbor in his work On the Perfection of the Spiritual Life. His aim here is explaining the perfection of the religious state and the episcopal state.
Necessary love of neighbor
The basic commandments is "You shall love your neighbor as yourself." From these follows three points regarding the love of our neighbor we must have:
First, it must be true love, that is, we must love him or her not in the sense that we may love chocolate or wine. When we love these we refer them to ourselves, whom we properly love. We must love our neighbors so as to will them good for their own sake, and not only inasmuch as they are pleasant or helpful to use.
Secondly, we must love our neighbor with an ordered love. Everyone loves his spiritual nature more than his bodily nature. This is evident from the fact that no one would prefer being an idiot to being blind. So also we must love the spiritual good of our neighbor more than his bodily good, and again, we must love his bodily good more than his external goods.
Thirdly, we must love our neighbors with a holy love, inasmuch as we must love both ourselves and them as made in the likeness of God, as ordered to God, and as called to communion with him. Since what is ordered to God is called holy, loving our neighbor for God's sake is a holy love.
Fourthly, we must love our neighbor with an efficacious love, that is, a love that proves itself by deeds, as St. John says, "let us not love in word or in speech, but in deed and in truth."
Perfect love of neighbor that is counseled
Love of neighbor can be perfect in three ways which are not obligatory
1. Love can be perfect with respect to its extensiveness, when we show love to all men, even when we are not strictly required to do so. Aquinas distinguishes three degrees of love with respect to extension: (1) the lowest degree is when we love only those who are close to us; (2) the second degree is when we love not only those who are relatives or are close to us in some other way, but men and women everywhere; (3) the third degree is when we show love even to our enemies, to those who hurt us–even when we wouldn't be obliged to show a particular love for them. E.g., when we could with justice wait for them to make amends, to go out of our way to seek reconciliation.
2. Love of neighbor can be perfect with respect to its intensity. This perfection is shown by what a person is ready to give up for the sake of his neighbor. Thomas distinguishes three levels here, corresponding to the three evangelical counsels: (1) some give up possessions for the sake of their fellow men and women; (2) some expose their body labor and fatigue, or to persecution for the sake of others; (3) some lay down their life for others; the closest thing to this dying for others is giving up one's own will for the sake of others. For since to be alive means to act on one's own, to give up one's will is like a kind of death.
3. Love of neighbor can be perfect with respect to its works. (1) Some procure the bodily good of others, by feeding them, clothing them, or healing them; (2) some procure the spiritual good of others, as by teaching, but such spiritual good as is on man's own level; (3) some procure the spiritual good of others that is on a divine level–giving them the divine teaching, bestowing the sacraments, etc. This belongs above all to bishops.