The expression "Love your neighbor as yourself" is equivalent to the phrase "Be perfect as your heavenly Father is perfect" Matthew 5:48.
Love your neighbor as yourself means to love good, means to expand our love to the others, in the good love our neighbor matters. The Good is expansive and therefore the good love.
In this love we expand our love to the other, our neighbor. It is like this that our neighbor becomes our brother.
The Good love is an excellence, a perfection and therefore a spiritual gift. This commandment is the commandment of excellence, be excellent as God is excellent, be perfect as God is perfect expression of Matthew 5:48.
The Old Law, the Ten Commandments, express the ethic and moral of the ancient world, but The Old Law has a weak point: when the truth and the life are opposed a commandment must be violated.
The Old Law is unattainable. That is why Christ left the Old Law for this new commandment. This is the commandment that makes us like God and gives us the gift of his grace.