Spiritual love is not something we produce within ourselves. It is not something we attain simply by willing it to be so. Love, and charity, come from the Lord. And the Lord will give us this life of charity provided only that we obey His commandments, and do not allow hatred to destroy this life. If we shun what is hateful, then the Lord will bless us with love.
Murder includes all forms of enmity, hatred and revenge.
When we act with enmity, when we act from hatred, we might imagine that we are acting only against our fellow human beings. It involves more than this, though. To act in this way is not only an evil against other people. It is also an evil against the Lord. That is what a sin is.