Sri Ramakrishna used to explain the true nature of the highest love through an incident from the Mahabharata.
Once, Arjuna became proud that there was none equal to him in love and devotion to his Lord and friend, Sri Krishna. The latter wanted to correct his attitude and took him for a walk one day. Soon they saw a strange Brahmana eating dry grasses as food, but who nevertheless had a sword dangling from his hip. Arjuna recognised him to be a pious Vaishnava, who won’t injure anyone, yet he was carrying a sword. When Arjuna asked the Brahmana for the reason, he said that he was carrying the sword to punish four persons if he happened to meet them. When Arjuna asked who they were, the Brahmana started listing them.
He said, “The first was the wretched Narada who permanently kept the Lord awake with his singing and music”. The Brahmana continued that the second offender was the imprudent Draupadi, who was thoughtless as to call the Brahmana’s beloved Lord just at the moment he was going for his dinner. He had to give up his food and go to the forest to save the Pandavas from the curse of sage Durwasa. The third was the heartless Prahlad, who did not hesitate for a moment to ask the Lord to enter the boiling cauldron of oil, to be trodden under the heavy foot of elephant and to break through the adamantine pillar. The Brahmana continued that the fourth offender was the wretched Arjuna to make the Lord assume the humble office of a charioteer of his vehicle in the great war of Kurukshetra.
Arjuna was amazed at the depth of the poor Brahmana’s devotion and love. At that moment, his pride vanished and he gave up thinking that he was the best devotee of the Lord.
According to Sri Ramakrishna, love is the highest which is expressed without expectation of anything in return.