Chapter 1, Verse 11
ayaneșu ca sarveşu
yathā-bhāgam avasthitāḥ
bhișmam evābhi-rakṣantu
bhavantaḥ sarva eva hi
"Therefore, all of you standing in your respective divisions in the different fronts of the battle, guard Bhishma."
Here Duryodhan addressed his people saying, "Whatever you do, never lose sight of Bhishma!" Why did he say that? He knew that the only person who could kill Bhishma, Shikandhini, was there in the Pandavas' army. She was the only one, who could kill Bhishma, whether he wanted it or not. This was because in her past life when she was Amba, she had wanted to marry Bhishma, and he had refused to marry her. Out of anger, she cursed Bhishma saying, "I will be the only one who will be able to kill you. You will die by my hand." She did her penance with one aim only: to kill Bhishma. So she was later born to the King Drupada, as a daughter. Drupada had actually wanted to have a son, and Lord Shiva had blessed him to have a son. Drupada said, "But I didn't get a son, I only got a daughter." He never liked her, but Lord Shiva's blessing couldn't be undone. Draupada only wanted a son to have his revenge on Drona. Of course, with Lord Shiva's blessing, the male quality was very strong in his daughter. Duryodhan knew that Bhishma would only put down his weapon if she came in front of him, because of the past life. That's why he said, "In every way protect Bhishma." Shikandhini represents knowledge and compassion. If knowledge arises, the knowledge of the Self, the knowledge of knowing and reaching God, all the other negative qualities will disappear, no? That's why Duryodhan said, "Protect Bhishma! Protect the ego! It doesn't matter what you do, protect him. He is our strength! To maintain that strength, we have to be around him, protecting him. We should not let Shikhandini come near him!"
Shikandhini was born for this one aim - but women were not allowed on the battlefield. And her only aim was to be on the battlefield. She went and did great penance before the war so that she could transform into a man. She did penance, but the penance was stopped many times and she was very disappointed. She prayed to Lord Shiva and said, "You promised that I would be a man, but just having the qualities of a man is not good enough. The other warriors will not allow me on the battlefield because my physical body is still like a woman's." So she continued her intense penance. Finally, there was a yaksha: a yaksha is not a demon, it was an entity who took pity on her and said, "Shikhandini, I have seen your penance. I felt pity for you. With my magical power, I will change you into a man. Actually, we will do a sex change." They didn't do any operations at that time. The yaksha said, "But there will be one condition: you will be a man for only one day. After that day, you will change back again to a woman." Shikandhini accepted and said, "Fine!" She was very happy. It was the ninth day of the war. She said, "I will try everything possible to kill Bhishma." From Shikandhini she became Shikandhi.
That night Krishna was talking to the Pandavas and said, "Only Shikandhi can kill Bhishma, nobody else!" At that moment, Shikandhi came and it was settled that the next day he would be in the same chariot as Arjuna. Bhishma would be killed. When Bhishma saw Shikandhi, even though she was in a man's body, he addressed her as a woman and said, "Lady Amba, fulfil your wish, the reason why you have come. I am putting down my weapon." He willingly put down his weapon, because for him, it was not Shikandhi, it was Amba, from her former life. He put down his weapon and she shot the first arrow into Bhishma. That's why in this verse Duryodhan said, "No matter what, there should not be any loopholes. You have to always be alert. If you see Shikandhi, drive her away from Bhishma with all your force." Otherwise, the Kauravas were not scared of anything from the Pandavas, because they knew that Bhishma could fight all of them. He was so powerful! The only fear they had was of Shikandhi.
Bhagavad Gita
