When you have self esteem aka a lack of self condemnation---it changes your esteem, love and compassion for others. When that self condemnation is present, it's not actually humility, not real humility---since the self condemnation gets psychologically projected onto the other, out there. So a person who values him/herself is kinder, more compassionate, more genuinely caring toward their friends, family and strangers.
The word selfishness needs to be examined ruthlessly----because often it's a word designed to manipulate people into being someone else's idea of respectable. It's a tool of intimidation, in order to force people to put on an act, to look 'as if.'
When you love and value yourself, and are then projecting loving acceptance outward instead of condemnation you'll see the manipulations of control freaks for what they are, even when they try to intimidate and control others by threatening to ridicule them as being selfish narcissists who only care about themselves.
When you dare to be who you are fearlessly, you won't be intimidated by such manipulators. Let them call you selfish---but you won't be going through life repressing your true thoughts, feelings and identity to fool control freaks into thinking you're the person they commanded you to be.
When you help others it will be authentic, because you truly care, not because you're fearful of being labeled selfish, a bad person in the eyes of manipulators. The guilt trips many people try to control you with need to be examined so you can be the real you...which is way better than being some repressed psycho's definition of an acceptable virtuous person. Real virtue doesn't chase approval or put up a false front to avoid ridicule.
Self esteem becomes love not only of self but of others too, because it is fearless. The virtuous don't scare. Instead of bowing weakly to a sick repressed society's tactics of control through intimidation, the virtuous stand strong in their own center, immovable.