Say we had a person who by unique circumstances never learned, gave or experienced love. If they did not understand love, how would convince them that love existed?
Watching others go though the motions of love; cuddling, laughing, smiling, sharing, may not induce love inside them. Love is also about that inner feeling that helps us differentiate the concept. However, science does not trust inside data, therefore love does not exist in terms of science, except as soft science. Love is more important in religion, which allows for inner experiences, that are not obvious by simply observing someone go through the motions, calling those motions, love.
Mr Spock tried to control his emotions so he could observe data without the bias of emotions. However, it is that internal integral bias that is foundation of love. Science may only be able to sees the external motions of love in actions and physiology, but lacks the needed internal bias focus for love and religion.