“The emblem of Hanuman on the flag of Arjuna is another sign of victory because Hanuman cooperated with Lord Rama in the battle between Rama and Ravana, and Lord Rama emerged victorious. Now both Rama and Hanuman were present on the chariot of Arjuna to help him. Lord Krishna is Rama Himself, and wherever Lord Rama is, His eternal servitor Hanuman and His eternal consort Sita, the goddess of fortune, are present. Therefore, Arjuna had no cause to fear any enemies whatsoever.” (Shrila Prabhupada, BG 1.20 Purport)
We find that in our material endeavors, we often invoke the name or memory of someone as a way of bringing good luck. Athletes often carry good luck charms given to them by legendary figures in their sport. They also remember the accomplishments of previous great athletes prior to having to perform. Politicians will often invoke the names of great leaders from the past when making an important speech.
These are all ways that we try to ensure success in our ventures. When entering a new field or starting a new task, it is best to consult those who have previously been able to triumph. The successful have the necessary experience and wisdom to help us achieve victory since they have gone through similar challenges. In the same way, in order to be successful in spiritual life, we must consult great devotees of the past.
To the normal person, Arjuna’s task prior to the start of the Kurukshetra War seemed to be that of a warrior trying to achieve victory for his side. In actuality, since he was following the direct orders of Lord Krishna, the Supreme Personality of Godhead, his task was actually that of performing devotional service to God. Because of this, Arjuna’s chariot was decorated with a flag bearing the emblem of Lord Hanuman.
In Lord Krishna’s previous incarnation as Lord Rama, there was a great demon named Ravana who had kidnapped Lord Rama’s wife, Sita. Hanuman, a Vanara (human-like monkey) and great devotee of Lord Rama, carried out the orders of the Lord and helped defeat Ravana and rescue Sita. Since Arjuna was also involved in a similar task of performing devotional service to the Lord, he made sure to invoke the memory of Krishna’s great devotee, Hanuman. In our normal everyday affairs, we tend to forget things that we do, services that we provide for people, and the things that others have done for us. God, on the other hand, never forgets service performed for Him. Hanuman was a pure devotee and helped the Lord, and Krishna never forgot it. He made sure that Hanuman would always be famous as a great devotee. He made sure the name of Hanuman would be synonymous with victory in devotional service.
So the lesson is that we should always remember the great devotees of the Lord and ask them for their mercy in helping us serve Krishna. Arjuna already had God acting as his charioteer, so he had no cause for concern. However, simply by remembering Hanuman, his success was guaranteed. This is God’s promise to us. By always remembering Krishna's great devotees and following the example they set forth, we will never meet defeat in our devotional service to the Lord.